Package: java.util

## Interface Map

- - ### Methods Summary

    Methods
    Return type | Name and parameters
    --- | ---
    `boolean` | `any(Closure predicate)` Iterates over the entries of a map, and checks whether a predicate is valid for at least one entry.
    `boolean` | `asBoolean()` Coerce a map instance to a boolean value.
    `Map` | `asImmutable()` A convenience method for creating an immutable Map.
    `Map` | `asSynchronized()` A convenience method for creating a synchronized Map.
    `Object` | `asType(Class clazz)` Coerces this map to the given type, using the map's keys as the public method names, and values as the implementation.
    `Map` | `asUnmodifiable()` Creates an unmodifiable view of a Map.
    `List` | `collect(Closure transform)` Iterates through this Map transforming each map entry into a new value using the `transform` closure returning a list of transformed values.
    `Collection` | `collect(Collection collector, Closure transform)` Iterates through this Map transforming each map entry into a new value using the `transform` closure returning the `collector` with all transformed values added to it.
    `Map` | `collectEntries(Closure transform)` Iterates through this Map transforming each entry using the `transform` closure and returning a map of the transformed entries.
    `Map` | `collectEntries(Map collector, Closure transform)` Iterates through this Map transforming each map entry using the `transform` closure returning a map of the transformed entries.
    `Collection` | `collectMany(Closure projection)` Projects each item from a source map to a result collection and concatenates (flattens) the resulting collections adding them into a collection.
    `Collection` | `collectMany(Collection collector, Closure projection)` Projects each item from a source map to a result collection and concatenates (flattens) the resulting collections adding them into the `collector`.
    `Number` | `count(Closure closure)` Counts the number of occurrences which satisfy the given closure from inside this map.
    `Map` | `countBy(Closure closure)` Groups the members of a map into groups determined by the supplied mapping closure and counts the frequency of the created groups.
    `Map` | `drop(int num)` Drops the given number of key/value pairs from the head of this map if they are available.
    `Map` | `dropWhile(Closure condition)` Create a suffix of the given Map by dropping as many entries as possible from the front of the original Map such that calling the given closure condition evaluates to true when passed each of the dropped entries (or key/value pairs).
    `Map` | `each(Closure closure)` Allows a Map to be iterated through using a closure.
    `Map` | `eachWithIndex(Closure closure)` Allows a Map to be iterated through using a closure.
    `boolean` | `equals(Map other)` Compares two Maps treating coerced numerical values as identical.
    `boolean` | `every(Closure predicate)` Iterates over the entries of a map, and checks whether a predicate is valid for all entries.
    `Entry` | `find(Closure closure)` Finds the first entry matching the closure condition.
    `Map` | `findAll(Closure closure)` Finds all entries matching the closure condition.
    `Object` | `findResult(Closure condition)` Returns the first non-null closure result found by passing each map entry to the closure, otherwise null is returned.
    `Object` | `findResult(Object defaultResult, Closure condition)` Returns the first non-null closure result found by passing each map entry to the closure, otherwise the defaultResult is returned.
    `Collection` | `findResults(Closure filteringTransform)` Iterates through the map transforming items using the supplied closure and collecting any non-null results.
    `Object` | `get(Object key, Object defaultValue)` Looks up an item in a Map for the given key and returns the value - unless there is no entry for the given key in which case add the default value to the map and return that.
    `Object` | `getAt(Object key)` Support the subscript operator for a Map.
    `Map` | `groupBy(Closure closure)` Groups the members of a map into sub maps determined by the supplied mapping closure.
    `Map` | `groupBy(Object closures)` Groups the members of a map into sub maps determined by the supplied mapping closures.
    `Map` | `groupBy(List closures)` Groups the members of a map into sub maps determined by the supplied mapping closures.
    `Map` | `groupEntriesBy(Closure closure)` Groups all map entries into groups determined by the supplied mapping closure.
    `Object` | `inject(Object initialValue, Closure closure)` Iterates through the given Map, passing in the initial value to the 2-arg Closure along with the first item (or 3-arg Closure along with the first key and value).
    `Map` | `intersect(Map right)` Create a Map composed of the intersection of both maps.
    `boolean` | `isCase(Object switchValue)` 'Case' implementation for maps which tests the groovy truth value obtained using the 'switch' operand as key.
    `Map` | `leftShift(Map other)` Overloads the left shift operator to provide an easy way to put one maps entries into another map.
    `Map` | `leftShift(Entry entry)` Overloads the left shift operator to provide an easy way to append Map.Entry values to a Map.
    `Entry` | `max(Closure closure)` Selects an entry in the map having the maximum calculated value as determined by the supplied closure.
    `Entry` | `min(Closure closure)` Selects an entry in the map having the minimum calculated value as determined by the supplied closure.
    `Map` | `minus(Map removeMe)` Create a Map composed of the entries of the first map minus the entries of the given map.
    `Map` | `plus(Collection entries)` Returns a new `Map` containing all entries from `self` and `entries`, giving precedence to `entries`.
    `Map` | `plus(Map right)` Returns a new `Map` containing all entries from `left` and `right`, giving precedence to `right`.
    `Map` | `putAll(Collection entries)` Provides an easy way to append multiple Map.Entry values to a Map.
    `Object` | `putAt(Object key, Object value)` A helper method to allow maps to work with subscript operators
    `boolean` | `removeAll(Closure condition)` Modifies this map by removing the elements that are matched according to the specified closure condition.
    `boolean` | `retainAll(Closure condition)` Modifies this map so that it retains only its elements that are matched according to the specified closure condition.
    `Map` | `reverseEach(Closure closure)` Allows a Map to be iterated through in reverse order using a closure.
    `Map` | `sort()` Sorts the elements from the given map into a new ordered Map using the natural ordering of the keys to determine the ordering.
    `Map` | `sort(Closure closure)` Sorts the elements from the given map into a new ordered map using the closure as a comparator to determine the ordering.
    `Map` | `sort(Comparator comparator)` Sorts the elements from the given map into a new ordered Map using the specified key comparator to determine the ordering.
    `SpreadMap` | `spread()` Synonym for Map#toSpreadMap().
    `Map` | `subMap(Object[] keys)` Creates a sub-Map containing the given keys.
    `Map` | `subMap(Collection keys)` Creates a sub-Map containing the given keys.
    `Map` | `take(int num)` Returns a new map containing the first `num` elements from the head of this map.
    `Map` | `takeWhile(Closure condition)` Returns the longest prefix of this Map where each entry (or key/value pair) when passed to the given closure evaluates to true.
    `String` | `toMapString()` Returns the string representation of this map.
    `String` | `toMapString(int maxSize)` Returns the string representation of this map.
    `Map` | `toSorted()` Sorts the elements from the given map into a new ordered map using a NumberAwareComparator on map entry values to determine the resulting order.
    `Map` | `toSorted(Closure condition)` Sorts the elements from the given map into a new ordered map using the supplied Closure condition as a comparator to determine the ordering.
    `Map` | `toSorted(Comparator comparator)` Sorts the elements from the given map into a new ordered map using the supplied comparator to determine the ordering.
    `SpreadMap` | `toSpreadMap()` Returns a new `SpreadMap` from this map.
    `Map` | `withDefault(Closure init)` Wraps a map using the decorator pattern with a wrapper that intercepts all calls to `get(key)`.

- - ### Methods Detail

    - #### public boolean any(Closure predicate)

      Iterates over the entries of a map, and checks whether a predicate is valid for at least one entry. If the closure takes one parameter then it will be passed the Map.Entry otherwise if the closure takes two parameters then it will be passed the key and the value.

          assert [2:3, 4:5, 5:10].any { key, value -> key * 2 == value }
          assert ![2:3, 4:5, 5:10].any { entry -> entry.key == entry.value * 2 }

      Parameters:
        `predicate` - the 1 or 2 arg closure predicate used for matching
      Returns:
        true if any entry in the map matches the closure predicate
      Since:
        1.5.0

    - #### public boolean asBoolean()

      Coerce a map instance to a boolean value. A map is coerced to false if it's empty, and to true otherwise.

          assert [:] as Boolean == false
          assert [a:2] as Boolean == true

      Returns:
        the boolean value
      Since:
        1.7.0

    - #### public Map asImmutable()

      A convenience method for creating an immutable Map.

      Returns:
        an unmodifiable view of a copy of the original, i.e. an effectively immutable copy
      Since:
        1.0
      See Also:
        List#asImmutable()
        Map#asUnmodifiable()

    - #### public Map asSynchronized()

      A convenience method for creating a synchronized Map.

      Returns:
        a synchronized Map
      Since:
        1.0
      See Also:
        Collections#synchronizedMap(java.util.Map)

    - #### public Object asType(Class clazz)

      Coerces this map to the given type, using the map's keys as the public method names, and values as the implementation. Typically the value would be a closure which behaves like the method implementation.

      Parameters:
        `clazz` - the target type
      Returns:
        a Proxy of the given type, which defers calls to this map's elements.
      Since:
        1.0

    - #### public Map asUnmodifiable()

      Creates an unmodifiable view of a Map.

      Returns:
        an unmodifiable view of the Map
      Since:
        2.5.0
      See Also:
        Collections#unmodifiableMap(java.util.Map)
        List#asUnmodifiable()

    - #### public List collect(Closure transform)

      Iterates through this Map transforming each map entry into a new value using the `transform` closure returning a list of transformed values.

          assert [a:1, b:2].collect { key, value -> key*value } == ["a", "bb"]
          assert [3:20, 2:30].collect { entry -> entry.key * entry.value } == [60, 60]

      Parameters:
        `transform` - the transformation closure which can take one (Map.Entry) or two (key, value) parameters
      Returns:
        the resultant list of transformed values
      Since:
        1.0

    - #### public Collection collect(Collection collector, Closure transform)

      Iterates through this Map transforming each map entry into a new value using the `transform` closure returning the `collector` with all transformed values added to it.

          assert [a:1, b:2].collect( [] as HashSet ) { key, value -> key*value } == ["a", "bb"] as Set
          assert [3:20, 2:30].collect( [] as HashSet ) { entry -> entry.key * entry.value } == [60] as Set

      Parameters:
        `collector` - the Collection to which transformed values are added
        `transform` - the transformation closure which can take one (Map.Entry) or two (key, value) parameters
      Returns:
        the collector with all transformed values added to it
      Since:
        1.0

    - #### public Map collectEntries(Closure transform)

      Iterates through this Map transforming each entry using the `transform` closure and returning a map of the transformed entries.

          assert [a:1, b:2].collectEntries { key, value -> [value, key] } == [1:'a', 2:'b']
          assert [a:1, b:2].collectEntries { key, value ->
              [(value*10): key.toUpperCase()] } == [10:'A', 20:'B']

      Note: When using the list-style of result, the behavior is '`def (key, value) = listResultFromClosure`'. While we strongly discourage using a list of size other than 2, Groovy's normal semantics apply in this case; throwing away elements after the second one and using null for the key or value for the case of a shortened list. If your Map doesn't support null keys or values, you might get a runtime error, e.g. NullPointerException or IllegalArgumentException.
      Parameters:
        `transform` - the closure used for transforming, which can take one (Map.Entry) or two (key, value) parameters and should return a Map.Entry, a Map or a two-element list containing the resulting key and value
      Returns:
        a Map of the transformed entries
      Since:
        1.7.9
      See Also:
        Map#collect(Collection, Closure)

    - #### public Map collectEntries(Map collector, Closure transform)

      Iterates through this Map transforming each map entry using the `transform` closure returning a map of the transformed entries.

          assert [a:1, b:2].collectEntries( [:] ) { k, v -> [v, k] } == [1:'a', 2:'b']
          assert [a:1, b:2].collectEntries( [30:'C'] ) { key, value ->
              [(value*10): key.toUpperCase()] } == [10:'A', 20:'B', 30:'C']

      Note: When using the list-style of result, the behavior is '`def (key, value) = listResultFromClosure`'. While we strongly discourage using a list of size other than 2, Groovy's normal semantics apply in this case; throwing away elements after the second one and using null for the key or value for the case of a shortened list. If your collector Map doesn't support null keys or values, you might get a runtime error, e.g. NullPointerException or IllegalArgumentException.
      Parameters:
        `collector` - the Map into which the transformed entries are put
        `transform` - the closure used for transforming, which can take one (Map.Entry) or two (key, value) parameters and should return a Map.Entry, a Map or a two-element list containing the resulting key and value
      Returns:
        the collector with all transformed values added to it
      Since:
        1.7.9
      See Also:
        Map#collect(Collection, Closure)

    - #### public Collection collectMany(Closure projection)

      Projects each item from a source map to a result collection and concatenates (flattens) the resulting collections adding them into a collection.

          def map = [bread:3, milk:5, butter:2]
          def result = map.collectMany{ k, v -> k.startsWith('b') ? k.toList() : [] }
          assert result == ['b', 'r', 'e', 'a', 'd', 'b', 'u', 't', 't', 'e', 'r']

      Parameters:
        `projection` - a projecting Closure returning a collection of items
      Returns:
        the collector with the projected collections concatenated (flattened) to it
      Since:
        1.8.8

    - #### public Collection collectMany(Collection collector, Closure projection)

      Projects each item from a source map to a result collection and concatenates (flattens) the resulting collections adding them into the `collector`.

          def map = [bread:3, milk:5, butter:2]
          def result = map.collectMany(['x']){ k, v -> k.startsWith('b') ? k.toList() : [] }
          assert result == ['x', 'b', 'r', 'e', 'a', 'd', 'b', 'u', 't', 't', 'e', 'r']

      Parameters:
        `collector` - an initial collection to add the projected items to
        `projection` - a projecting Closure returning a collection of items
      Returns:
        the collector with the projected collections concatenated (flattened) to it
      Since:
        1.8.8

    - #### public Number count(Closure closure)

      Counts the number of occurrences which satisfy the given closure from inside this map. If the closure takes one parameter then it will be passed the Map.Entry. Otherwise, the closure should take two parameters and will be passed the key and value.

      Example usage:

          assert [a:1, b:1, c:2, d:2].count{ k,v -> k == 'a' || v == 2 } == 3

      Parameters:
        `closure` - a 1 or 2 arg Closure condition applying on the entries
      Returns:
        the number of occurrences
      Since:
        1.8.0

    - #### public Map countBy(Closure closure)

      Groups the members of a map into groups determined by the supplied mapping closure and counts the frequency of the created groups. The closure will be passed a Map.Entry or key and value (depending on the number of parameters the closure accepts) and should return the key that each item should be grouped under. The resulting map will have an entry for each 'group' key returned by the closure, with values being the frequency counts for that 'group'.

          def result = [a:1,b:2,c:3,d:4,e:5].countBy { it.value % 2 }
          assert result == [0:2, 1:3]

      Parameters:
        `closure` - a closure mapping entries to frequency count keys
      Returns:
        a new Map grouped by keys with frequency counts
      Since:
        1.8.0

    - #### public Map drop(int num)

      Drops the given number of key/value pairs from the head of this map if they are available.

          def strings = [ 'a':10, 'b':20, 'c':30 ]
          assert strings.drop( 0 ) == [ 'a':10, 'b':20, 'c':30 ]
          assert strings.drop( 2 ) == [ 'c':30 ]
          assert strings.drop( 5 ) == [:]

      If the map instance does not have ordered keys, then this function could drop a random `num` entries. Groovy by default uses LinkedHashMap, so this shouldn't be an issue in the main.
      Parameters:
        `num` - the number of elements to drop from this map
      Returns:
        a map consisting of all key/value pairs of this map except the first `num` ones, or else the empty map, if this map has less than `num` elements.
      Since:
        1.8.1

    - #### public Map dropWhile(Closure condition)

      Create a suffix of the given Map by dropping as many entries as possible from the front of the original Map such that calling the given closure condition evaluates to true when passed each of the dropped entries (or key/value pairs).

          def shopping = [milk:1, bread:2, chocolate:3]
          assert shopping.dropWhile{ it.key.size() < 6 } == [chocolate:3]
          assert shopping.dropWhile{ it.value % 2 } == [bread:2, chocolate:3]
          assert shopping.dropWhile{ k, v -> k.size() + v <= 7 } == [chocolate:3]

      If the map instance does not have ordered keys, then this function could appear to drop random entries. Groovy by default uses LinkedHashMap, so this shouldn't be an issue in the main.
      Parameters:
        `condition` - a 1 (or 2) arg Closure that must evaluate to true for the entry (or key and value) to continue dropping elements
      Returns:
        the shortest suffix of the given Map such that the given closure condition evaluates to true for each element dropped from the front of the Map
      Since:
        1.8.7

    - #### public Map each(Closure closure)

      Allows a Map to be iterated through using a closure. If the closure takes one parameter then it will be passed the Map.Entry otherwise if the closure takes two parameters then it will be passed the key and the value.

          def result = ""
          [a:1, b:3].each { key, value -> result += "$key$value" }
          assert result == "a1b3"

          def result = ""
          [a:1, b:3].each { entry -> result += entry }
          assert result == "a=1b=3"

      In general, the order in which the map contents are processed cannot be guaranteed. In practise, specialized forms of Map, e.g. a TreeMap will have its contents processed according to the natural ordering of the map.
      Parameters:
        `closure` - the 1 or 2 arg closure applied on each entry of the map
      Returns:
        returns the self parameter
      Since:
        1.5.0

    - #### public Map eachWithIndex(Closure closure)

      Allows a Map to be iterated through using a closure. If the closure takes two parameters then it will be passed the Map.Entry and the item's index (a counter starting at zero) otherwise if the closure takes three parameters then it will be passed the key, the value, and the index.

          def result = ""
          [a:1, b:3].eachWithIndex { key, value, index -> result += "$index($key$value)" }
          assert result == "0(a1)1(b3)"

          def result = ""
          [a:1, b:3].eachWithIndex { entry, index -> result += "$index($entry)" }
          assert result == "0(a=1)1(b=3)"

      Parameters:
        `closure` - a 2 or 3 arg Closure to operate on each item
      Returns:
        the self Object
      Since:
        1.5.0

    - #### public boolean equals(Map other)

      Compares two Maps treating coerced numerical values as identical.

      Example usage:

          assert [a:2, b:3] == [a:2L, b:3.0]

      Parameters:
        `other` - the Map being compared to
      Returns:
        `true` if the contents of both maps are identical
      Since:
        1.8.0

    - #### public boolean every(Closure predicate)

      Iterates over the entries of a map, and checks whether a predicate is valid for all entries. If the closure takes one parameter then it will be passed the Map.Entry otherwise if the closure takes two parameters then it will be passed the key and the value.

          def map = [a:1, b:2.0, c:2L]
          assert !map.every { key, value -> value instanceof Integer }
          assert map.every { entry -> entry.value instanceof Number }

      Parameters:
        `predicate` - the 1 or 2 arg Closure predicate used for matching
      Returns:
        true if every entry of the map matches the closure predicate
      Since:
        1.5.0

    - #### public Entry find(Closure closure)

      Finds the first entry matching the closure condition. If the closure takes two parameters, the entry key and value are passed. If the closure takes one parameter, the Map.Entry object is passed.

          assert [a:1, b:3].find { it.value == 3 }.key == "b"

      Parameters:
        `closure` - a 1 or 2 arg Closure condition
      Returns:
        the first Object found
      Since:
        1.0

    - #### public Map findAll(Closure closure)

      Finds all entries matching the closure condition. If the closure takes one parameter then it will be passed the Map.Entry. Otherwise if the closure should take two parameters, which will be the key and the value.

      If the `self` map is one of TreeMap, LinkedHashMap, Hashtable or Properties, the returned Map will preserve that type, otherwise a HashMap will be returned.

      Example usage:

          def result = [a:1, b:2, c:4, d:5].findAll { it.value % 2 == 0 }
          assert result.every { it instanceof Map.Entry }
          assert result*.key == ["b", "c"]
          assert result*.value == [2, 4]

      Parameters:
        `closure` - a 1 or 2 arg Closure condition applying on the entries
      Returns:
        a new subMap
      Since:
        1.0

    - #### public Object findResult(Closure condition)

      Returns the first non-null closure result found by passing each map entry to the closure, otherwise null is returned. If the closure takes two parameters, the entry key and value are passed. If the closure takes one parameter, the Map.Entry object is passed.

          assert "Found b:3" == [a:1, b:3].findResult { if (it.value == 3) return "Found ${it.key}:${it.value}" }
          assert null == [a:1, b:3].findResult { if (it.value == 9) return "Found ${it.key}:${it.value}" }
          assert "Found a:1" == [a:1, b:3].findResult { k, v -> if (k.size() + v == 2) return "Found $k:$v" }

      Parameters:
        `condition` - a 1 or 2 arg Closure that returns a non-null value when processing should stop and a value should be returned
      Returns:
        the first non-null result collected by calling the closure, or null if no such result was found
      Since:
        1.7.5

    - #### public Object findResult(Object defaultResult, Closure condition)

      Returns the first non-null closure result found by passing each map entry to the closure, otherwise the defaultResult is returned. If the closure takes two parameters, the entry key and value are passed. If the closure takes one parameter, the Map.Entry object is passed.

          assert "Found b:3" == [a:1, b:3].findResult("default") { if (it.value == 3) return "Found ${it.key}:${it.value}" }
          assert "default" == [a:1, b:3].findResult("default") { if (it.value == 9) return "Found ${it.key}:${it.value}" }
          assert "Found a:1" == [a:1, b:3].findResult("default") { k, v -> if (k.size() + v == 2) return "Found $k:$v" }

      Parameters:
        `defaultResult` - an Object that should be returned if all closure results are null
        `condition` - a 1 or 2 arg Closure that returns a non-null value when processing should stop and a value should be returned
      Returns:
        the first non-null result collected by calling the closure, or the defaultResult if no such result was found
      Since:
        1.7.5

    - #### public Collection findResults(Closure filteringTransform)

      Iterates through the map transforming items using the supplied closure and collecting any non-null results. If the closure takes two parameters, the entry key and value are passed. If the closure takes one parameter, the Map.Entry object is passed.

      Example:

          def map = [a:1, b:2, hi:2, cat:3, dog:2]
          def result = map.findResults { k, v -> k.size() == v ? "Found $k:$v" : null }
          assert result == ["Found a:1", "Found hi:2", "Found cat:3"]

      Parameters:
        `filteringTransform` - a 1 or 2 arg Closure that should return either a non-null transformed value or null for items which should be discarded
      Returns:
        the list of non-null transformed values
      Since:
        1.8.1

    - #### public Object get(Object key, Object defaultValue)

      Looks up an item in a Map for the given key and returns the value - unless there is no entry for the given key in which case add the default value to the map and return that.

          def map=[:]
          map.get("a", []) << 5
          assert map == [a:[5]]

      Parameters:
        `key` - the key to lookup the value of
        `defaultValue` - the value to return and add to the map for this key if there is no entry for the given key
      Returns:
        the value of the given key or the default value, added to the map if the key did not exist
      Since:
        1.0

    - #### public Object getAt(Object key)

      Support the subscript operator for a Map.

          def map = [a:10]
          assert map["a"] == 10

      Parameters:
        `key` - an Object as a key for the map
      Returns:
        the value corresponding to the given key
      Since:
        1.0

    - #### public Map groupBy(Closure closure)

      Groups the members of a map into sub maps determined by the supplied mapping closure. The closure will be passed a Map.Entry or key and value (depending on the number of parameters the closure accepts) and should return the key that each item should be grouped under. The resulting map will have an entry for each 'group' key returned by the closure, with values being the map members from the original map that belong to each group. (If instead of a map, you want a list of map entries use {code}groupEntriesBy{code}.)

      If the `self` map is one of TreeMap, Hashtable or Properties, the returned Map will preserve that type, otherwise a LinkedHashMap will be returned.

          def result = [a:1,b:2,c:3,d:4,e:5,f:6].groupBy { it.value % 2 }
          assert result == [0:[b:2, d:4, f:6], 1:[a:1, c:3, e:5]]

      Parameters:
        `closure` - a closure mapping entries on keys
      Returns:
        a new Map grouped by keys
      Since:
        1.0

    - #### public Map groupBy(Object closures)

      Groups the members of a map into sub maps determined by the supplied mapping closures. Each closure will be passed a Map.Entry or key and value (depending on the number of parameters the closure accepts) and should return the key that each item should be grouped under. The resulting map will have an entry for each 'group path' returned by all closures, with values being the map members from the original map that belong to each such 'group path'. If the `self` map is one of TreeMap, Hashtable, or Properties, the returned Map will preserve that type, otherwise a LinkedHashMap will be returned.

          def result = [a:1,b:2,c:3,d:4,e:5,f:6].groupBy({ it.value % 2 }, { it.key.next() })
          assert result == [1:[b:[a:1], d:[c:3], f:[e:5]], 0:[c:[b:2], e:[d:4], g:[f:6]]]

      If an empty array of closures is supplied the IDENTITY Closure will be used.
      Parameters:
        `closures` - an array of closures that map entries on keys
      Returns:
        a new map grouped by keys on each criterion
      Since:
        1.8.1
      See Also:
        Closure#IDENTITY

    - #### public Map groupBy(List closures)

      Groups the members of a map into sub maps determined by the supplied mapping closures. Each closure will be passed a Map.Entry or key and value (depending on the number of parameters the closure accepts) and should return the key that each item should be grouped under. The resulting map will have an entry for each 'group path' returned by all closures, with values being the map members from the original map that belong to each such 'group path'. If the `self` map is one of TreeMap, Hashtable, or Properties, the returned Map will preserve that type, otherwise a LinkedHashMap will be returned.

          def result = [a:1,b:2,c:3,d:4,e:5,f:6].groupBy([{ it.value % 2 }, { it.key.next() }])
          assert result == [1:[b:[a:1], d:[c:3], f:[e:5]], 0:[c:[b:2], e:[d:4], g:[f:6]]]

      If an empty list of closures is supplied the IDENTITY Closure will be used.
      Parameters:
        `closures` - a list of closures that map entries on keys
      Returns:
        a new map grouped by keys on each criterion
      Since:
        1.8.1
      See Also:
        Closure#IDENTITY

    - #### public Map groupEntriesBy(Closure closure)

      Groups all map entries into groups determined by the supplied mapping closure. The closure will be passed a Map.Entry or key and value (depending on the number of parameters the closure accepts) and should return the key that each item should be grouped under. The resulting map will have an entry for each 'group' key returned by the closure, with values being the list of map entries that belong to each group. (If instead of a list of map entries, you want an actual map use {code}groupBy{code}.)

          def result = [a:1,b:2,c:3,d:4,e:5,f:6].groupEntriesBy { it.value % 2 }
          assert result[0]*.key == ["b", "d", "f"]
          assert result[1]*.value == [1, 3, 5]

      Parameters:
        `closure` - a 1 or 2 arg Closure mapping entries on keys
      Returns:
        a new Map grouped by keys
      Since:
        1.5.2

    - #### public Object inject(Object initialValue, Closure closure)

      Iterates through the given Map, passing in the initial value to the 2-arg Closure along with the first item (or 3-arg Closure along with the first key and value). The result is passed back (injected) into the closure along with the second item. The new result is injected back into the closure along with the third item and so on until the entire collection has been used. Also known as `foldLeft` or `reduce` in functional parlance. Examples:

          def map = [a:1, b:2, c:3]
          assert map.inject([]) { list, k, v ->
            list + [k] * v
          } == ['a', 'b', 'b', 'c', 'c', 'c']

      Parameters:
        `initialValue` - some initial value
        `closure` - a 2 or 3 arg Closure
      Returns:
        the result of the last closure call
      Since:
        1.8.1

    - #### public Map intersect(Map right)

      Create a Map composed of the intersection of both maps. Any entries that exist in both maps are added to the resultant map.

          assert [4:4,5:5] == [1:1,2:2,3:3,4:4,5:5].intersect([4:4,5:5,6:6,7:7,8:8])

          assert [1: 1, 2: 2, 3: 3, 4: 4].intersect( [1: 1.0, 2: 2, 5: 5] ) == [1:1, 2:2]

      Parameters:
        `right` - a map
      Returns:
        a Map as an intersection of both maps
      Since:
        1.7.4

    - #### public boolean isCase(Object switchValue)

      'Case' implementation for maps which tests the groovy truth value obtained using the 'switch' operand as key. For example:

          switch( 'foo' ) {
            case [foo:true, bar:false]:
              assert true
              break
            default:
              assert false
          }

      Parameters:
        `switchValue` - the switch value
      Returns:
        the groovy truth value from caseValue corresponding to the switchValue key
      Since:
        1.7.6

    - #### public Map leftShift(Map other)

      Overloads the left shift operator to provide an easy way to put one maps entries into another map. This allows the compact syntax `map1 << map2`; otherwise it's just a synonym for `putAll` though it returns the original map rather than being a `void` method. Example usage:

          def map = [a:1, b:2]
          map << [c:3, d:4]
          assert map == [a:1, b:2, c:3, d:4]

      Parameters:
        `other` - another Map whose entries should be added to the original Map.
      Returns:
        same map, after the values have been added to it.
      Since:
        1.7.2

    - #### public Map leftShift(Entry entry)

      Overloads the left shift operator to provide an easy way to append Map.Entry values to a Map.

      Parameters:
        `entry` - a Map.Entry to be added to the Map.
      Returns:
        same map, after the value has been added to it.
      Since:
        1.6.0

    - #### public Entry max(Closure closure)

      Selects an entry in the map having the maximum calculated value as determined by the supplied closure. If more than one entry has the maximum value, an arbitrary choice is made between the entries having the maximum value.

      If the closure has two parameters it is used like a traditional Comparator. I.e. it should compare its two parameters for order, returning a negative integer, zero, or a positive integer when the first parameter is less than, equal to, or greater than the second respectively. Otherwise, the Closure is assumed to take a single parameter and return a Comparable (typically an Integer) which is then used for further comparison. An example:

          def zoo = [monkeys:6, lions:5, tigers:7]
          def mostCommonEntry = zoo.max{ it.value }
          assert mostCommonEntry.value == 7
          def leastCommonEntry = zoo.max{ a, b -> b.value <=> a.value } // double negative!
          assert leastCommonEntry.value == 5

      Edge case for multiple max values:

          def zoo = [monkeys:6, lions:5, tigers:7]
          def lengthOfNamePlusNumber = { e -> e.key.size() + e.value }
          def ans = zoo.max(lengthOfNamePlusNumber) // one of [monkeys:6, tigers:7]
          assert lengthOfNamePlusNumber(ans) == 13

      Parameters:
        `closure` - a 1 or 2 arg Closure used to determine the correct ordering
      Returns:
        the Map.Entry having the maximum value as determined by the closure
      Since:
        1.7.6

    - #### public Entry min(Closure closure)

      Selects an entry in the map having the minimum calculated value as determined by the supplied closure. If more than one entry has the minimum value, an arbitrary choice is made between the entries having the minimum value.

      If the closure has two parameters it is used like a traditional Comparator. I.e. it should compare its two parameters for order, returning a negative integer, zero, or a positive integer when the first parameter is less than, equal to, or greater than the second respectively. Otherwise, the Closure is assumed to take a single parameter and return a Comparable (typically an Integer) which is then used for further comparison.

          def zoo = [monkeys:6, lions:5, tigers:7]
          def leastCommonEntry = zoo.min{ it.value }
          assert leastCommonEntry.value == 5
          def mostCommonEntry = zoo.min{ a, b -> b.value <=> a.value } // double negative!
          assert mostCommonEntry.value == 7

      Edge case for multiple min values:

          def zoo = [monkeys:6, lions:5, tigers:7]
          def lastCharOfName = { e -> e.key[-1] }
          def ans = zoo.min(lastCharOfName) // some random entry
          assert lastCharOfName(ans) == 's'

      Parameters:
        `closure` - a 1 or 2 arg Closure used to determine the correct ordering
      Returns:
        the Map.Entry having the minimum value as determined by the closure
      Since:
        1.7.6

    - #### public Map minus(Map removeMe)

      Create a Map composed of the entries of the first map minus the entries of the given map.

      Parameters:
        `removeMe` - the entries to remove from the map
      Returns:
        the resulting map
      Since:
        1.7.4

    - #### public Map plus(Collection entries)

      Returns a new `Map` containing all entries from `self` and `entries`, giving precedence to `entries`. Any keys appearing in both Maps will appear in the resultant map with values from the `entries` operand. If `self` map is one of TreeMap, LinkedHashMap, Hashtable or Properties, the returned Map will preserve that type, otherwise a HashMap will be returned.

      Parameters:
        `entries` - a Collection of Map.Entry items to be added to the Map.
      Returns:
        a new Map containing all key, value pairs from self and entries
      Since:
        1.6.1

    - #### public Map plus(Map right)

      Returns a new `Map` containing all entries from `left` and `right`, giving precedence to `right`. Any keys appearing in both Maps will appear in the resultant map with values from the `right` operand. If the `left` map is one of TreeMap, LinkedHashMap, Hashtable or Properties, the returned Map will preserve that type, otherwise a HashMap will be returned.

      Roughly equivalent to `Map m = new HashMap(); m.putAll(left); m.putAll(right); return m;` but with some additional logic to preserve the `left` Map type for common cases as described above.

          assert [a:10, b:20] + [a:5, c:7] == [a:5, b:20, c:7]

      Parameters:
        `right` - a Map
      Returns:
        a new Map containing all entries from left and right
      Since:
        1.5.0

    - #### public Map putAll(Collection entries)

      Provides an easy way to append multiple Map.Entry values to a Map.

      Parameters:
        `entries` - a Collection of Map.Entry items to be added to the Map.
      Returns:
        the same map, after the items have been added to it.
      Since:
        1.6.1

    - #### public Object putAt(Object key, Object value)

      A helper method to allow maps to work with subscript operators

      Parameters:
        `key` - an Object as a key for the map
        `value` - the value to put into the map
      Returns:
        the value corresponding to the given key
      Since:
        1.0

    - #### public boolean removeAll(Closure condition)

      Modifies this map by removing the elements that are matched according to the specified closure condition. If the closure takes one parameter then it will be passed the `Map.Entry`. Otherwise the closure should take two parameters, which will be the key and the value.

          def map = [a:1, b:2]
          map.removeAll { k,v -> k == 'b' }
          assert map == [a:1]

      See also `findAll` when wanting to produce a new map containing items which match some criteria but leaving the original map unchanged.
      Parameters:
        `condition` - a 1 or 2 arg Closure condition applying on the entries
      Returns:
        `true` if this map changed as a result of the call
      Since:
        2.5.0

    - #### public boolean retainAll(Closure condition)

      Modifies this map so that it retains only its elements that are matched according to the specified closure condition. In other words, removes from this map all of its elements that don't match. If the closure takes one parameter then it will be passed the `Map.Entry`. Otherwise the closure should take two parameters, which will be the key and the value.

          def map = [a:1, b:2]
          map.retainAll { k,v -> k == 'b' }
          assert map == [b:2]

      See also `findAll` when wanting to produce a new map containing items which match some criteria but leaving the original map unchanged.
      Parameters:
        `condition` - a 1 or 2 arg Closure condition applying on the entries
      Returns:
        `true` if this map changed as a result of the call
      Since:
        2.5.0

    - #### public Map reverseEach(Closure closure)

      Allows a Map to be iterated through in reverse order using a closure. In general, the order in which the map contents are processed cannot be guaranteed. In practise, specialized forms of Map, e.g. a TreeMap will have its contents processed according to the reverse of the natural ordering of the map.

      Parameters:
        `closure` - the 1 or 2 arg closure applied on each entry of the map
      Returns:
        returns the self parameter
      Since:
        1.7.2
      See Also:
        Map#each(Closure)

    - #### public Map sort()

      Sorts the elements from the given map into a new ordered Map using the natural ordering of the keys to determine the ordering. The original map is unchanged.

          map = [ba:3, cz:6, ab:5].sort()
          assert map*.value == [5, 3, 6]

      Returns:
        the sorted map
      Since:
        1.7.2

    - #### public Map sort(Closure closure)

      Sorts the elements from the given map into a new ordered map using the closure as a comparator to determine the ordering. The original map is unchanged.

          def map = [a:5, b:3, c:6, d:4].sort { a, b -> a.value <=> b.value }
          assert map == [b:3, d:4, a:5, c:6]

      Parameters:
        `closure` - a Closure used as a comparator
      Returns:
        the sorted map
      Since:
        1.6.0

    - #### public Map sort(Comparator comparator)

      Sorts the elements from the given map into a new ordered Map using the specified key comparator to determine the ordering. The original map is unchanged.

          def map = [ba:3, cz:6, ab:5].sort({ a, b -> a[-1] <=> b[-1] } as Comparator)
          assert map*.value == [3, 5, 6]

      Parameters:
        `comparator` - a Comparator
      Returns:
        the sorted map
      Since:
        1.7.2

    - #### public SpreadMap spread()

      Synonym for Map#toSpreadMap().

      Returns:
        a newly created SpreadMap
      Since:
        1.0

    - #### public Map subMap(Object[] keys)

      Creates a sub-Map containing the given keys. This method is similar to List.subList() but uses keys rather than index ranges. The original map is unaltered.

          def orig = [1:10, 2:20, 3:30, 4:40]
          assert orig.subMap([1, 3] as int[]) == [1:10, 3:30]
          assert orig.subMap([2, 4] as Integer[]) == [2:20, 4:40]
          assert orig.size() == 4

      Parameters:
        `keys` - an array of keys
      Returns:
        a new Map containing the given keys
      Since:
        2.1.0

    - #### public Map subMap(Collection keys)

      Creates a sub-Map containing the given keys. This method is similar to List.subList() but uses keys rather than index ranges.

          assert [1:10, 2:20, 4:40].subMap( [2, 4] ) == [2:20, 4:40]

      Parameters:
        `keys` - a Collection of keys
      Returns:
        a new Map containing the given keys
      Since:
        1.0

    - #### public Map take(int num)

      Returns a new map containing the first `num` elements from the head of this map. If the map instance does not have ordered keys, then this function could return a random `num` entries. Groovy by default uses LinkedHashMap, so this shouldn't be an issue in the main.

          def strings = [ 'a':10, 'b':20, 'c':30 ]
          assert strings.take( 0 ) == [:]
          assert strings.take( 2 ) == [ 'a':10, 'b':20 ]
          assert strings.take( 5 ) == [ 'a':10, 'b':20, 'c':30 ]

      Parameters:
        `num` - the number of elements to take from this map
      Returns:
        a new map consisting of the first `num` elements of this map, or else the whole map if it has less then `num` elements.
      Since:
        1.8.1

    - #### public Map takeWhile(Closure condition)

      Returns the longest prefix of this Map where each entry (or key/value pair) when passed to the given closure evaluates to true.

          def shopping = [milk:1, bread:2, chocolate:3]
          assert shopping.takeWhile{ it.key.size() < 6 } == [milk:1, bread:2]
          assert shopping.takeWhile{ it.value % 2 } == [milk:1]
          assert shopping.takeWhile{ k, v -> k.size() + v <= 7 } == [milk:1, bread:2]

      If the map instance does not have ordered keys, then this function could appear to take random entries. Groovy by default uses LinkedHashMap, so this shouldn't be an issue in the main.
      Parameters:
        `condition` - a 1 (or 2) arg Closure that must evaluate to true for the entry (or key and value) to continue taking elements
      Returns:
        a prefix of the given Map where each entry (or key/value pair) passed to the given closure evaluates to true
      Since:
        1.8.7

    - #### public String toMapString()

      Returns the string representation of this map. The string displays the contents of the map, i.e. `[one:1, two:2, three:3]`.

      Returns:
        the string representation
      Since:
        1.0

    - #### public String toMapString(int maxSize)

      Returns the string representation of this map. The string displays the contents of the map, i.e. `[one:1, two:2, three:3]`.

      Parameters:
        `maxSize` - stop after approximately this many characters and append '...'
      Returns:
        the string representation
      Since:
        1.0

    - #### public Map toSorted()

      Sorts the elements from the given map into a new ordered map using a NumberAwareComparator on map entry values to determine the resulting order. `NumberAwareComparator` has special treatment for numbers but otherwise uses the natural ordering of the Iterator elements. The original map is unchanged.

          def map = [a:5L, b:3, c:6, d:4.0].toSorted()
          assert map.toString() == '[b:3, d:4.0, a:5, c:6]'

      Returns:
        the sorted map
      Since:
        2.4.0

    - #### public Map toSorted(Closure condition)

      Sorts the elements from the given map into a new ordered map using the supplied Closure condition as a comparator to determine the ordering. The original map is unchanged.

      If the closure has two parameters it is used like a traditional Comparator. I.e. it should compare its two entry parameters for order, returning a negative integer, zero, or a positive integer when the first parameter is less than, equal to, or greater than the second respectively. Otherwise, the Closure is assumed to take a single entry parameter and return a Comparable (typically an Integer) which is then used for further comparison.

          def map = [a:5, b:3, c:6, d:4].toSorted { a, b -> a.value <=> b.value }
          assert map.toString() == '[b:3, d:4, a:5, c:6]'

      Parameters:
        `condition` - a Closure used as a comparator
      Returns:
        the sorted map
      Since:
        2.4.0

    - #### public Map toSorted(Comparator comparator)

      Sorts the elements from the given map into a new ordered map using the supplied comparator to determine the ordering. The original map is unchanged.

          def keyComparator = [compare: { e1, e2 -> e1.key <=> e2.key }] as Comparator
          def valueComparator = [compare: { e1, e2 -> e1.value <=> e2.value }] as Comparator
          def map1 = [a:5, b:3, d:4, c:6].toSorted(keyComparator)
          assert map1.toString() == '[a:5, b:3, c:6, d:4]'
          def map2 = [a:5, b:3, d:4, c:6].toSorted(valueComparator)
          assert map2.toString() == '[b:3, d:4, a:5, c:6]'

      Parameters:
        `comparator` - a Comparator used for the comparison
      Returns:
        the sorted map
      Since:
        2.4.0

    - #### public SpreadMap toSpreadMap()

      Returns a new `SpreadMap` from this map.

      The example below shows the various possible use cases:

          def fn(Map m) { return m.a + m.b + m.c + m.d }

          assert fn(a:1, b:2, c:3, d:4) == 10
          assert fn(a:1, *:[b:2, c:3], d:4) == 10
          assert fn([a:1, b:2, c:3, d:4].toSpreadMap()) == 10
          assert fn((['a', 1, 'b', 2, 'c', 3, 'd', 4] as Object[]).toSpreadMap()) == 10
          assert fn(['a', 1, 'b', 2, 'c', 3, 'd', 4].toSpreadMap()) == 10
          assert fn(['abcd'.toList(), 1..4].transpose().flatten().toSpreadMap()) == 10

      Note that toSpreadMap() is not normally used explicitly but under the covers by Groovy.
      Returns:
        a newly created SpreadMap if this map is not null and its size is positive.
      Since:
        1.0
      See Also:
        SpreadMap#SpreadMap(java.util.Map)

    - #### public Map withDefault(Closure init)

      Wraps a map using the decorator pattern with a wrapper that intercepts all calls to `get(key)`. If an unknown key is found, a default value will be stored into the Map before being returned. The default value stored will be the result of calling the supplied Closure with the key as the parameter to the Closure. Example usage:

          def map = [a:1, b:2].withDefault{ k -> k.toCharacter().isLowerCase() ? 10 : -10 }
          def expected = [a:1, b:2, c:10, D:-10]
          assert expected.every{ e -> e.value == map[e.key] }

          def constMap = [:].withDefault{ 42 }
          assert constMap.foo == 42
          assert constMap.size() == 1

      Parameters:
        `init` - a Closure which is passed the unknown key
      Returns:
        the wrapped Map
      Since:
        1.7.1