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# Mean
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<br>
Transforms for computing the arithmetic mean of the elements in a collection,
or the mean of the values associated with each key in a collection of key-value pairs.

* `Mean.globally()` returns a transform that then returns a collection whose contents is the mean of the input collection's elements. If there are no elements in the input collection, it returns 0.
* `Mean.perKey()` returns a transform that returns a collection that contains an output element mapping each distinct key in the input collection to the mean of the values associated with that key in the input collection.

## Examples
**Example 1**: get the mean of a `PCollection` of `Longs`.

```java
PCollection<Double> input = ...;
PCollection<Double> mean = input.apply(Mean.globally());
```

**Example 2**: calculate the mean of the `Integers` associated with each unique key (which is of type `String`).

```java
PCollection<KV<String, Integer>> input = ...;
PCollection<KV<String, Integer>> meanPerKey =
     input.apply(Mean.perKey());
```

## Related transforms 
* [Max]({{ site.baseurl }}/documentation/transforms/java/aggregation/max)
  for computing maximum values in a collection
* [Min]({{ site.baseurl }}/documentation/transforms/java/aggregation/min)
  for computing maximum values in a collection
* [Combine]({{ site.baseurl }}/documentation/transforms/java/aggregation/combine)
  for combining all values associated with a key to a single result