# Shiny

#### John Coene

#### 2019-04-09

`sigmajs` goes hand in hand with Shiny. As stated in the wiki, sigma.js is “interactivity oriented” and therefore plays ideally in apps.

See it in action

Another good example of the package in the wild is chirp.sh.

## Features

- Proxies
- Events

`simgajs` lets you dynamically interact with the graph, that is, add/remove/customise without redrawing the whole graph: these functions all end in `_p`. The package also lets you catch how the user interacts with your graph.

## Proxies

- Add one or multiple nodes or edges.
- Remove one or multiple nodes or edges.
- Add nodes or edges with a given delay.
- Enable nodes drag.
- Start/kill/restart force layout.
- Refresh the graph.
- Zoom on a node.
- Export the graph to SVG or image format.

### Walkthrough

Here I mainly talk you through shiny proxies in general and the `add-nodes` demo.

Let’s start by building a simple Shiny app that includes a basic `sigmajs` graph.

    library(shiny)
    library(sigmajs)

    nodes <- sg_make_nodes()
    edges <- sg_make_edges(nodes)

    ui <- fluidPage(sigmajsOutput("sg")) # bare bone UI

    server <- function(input, output){
      output$sg <- renderSigmajs({
        sigmajs() %>%
          sg_nodes(nodes, id, size, color) %>%
          sg_edges(edges, id, source, target)
      })
    }

    shinyApp(ui, server) # run

Now that we have a simple app going we can look at playing with proxies. The layout looks a bit rubbish, we can add a proxy to let the user trigger the forceAtlas2 layout.

    nodes <- sg_make_nodes()
    edges <- sg_make_edges(nodes)

    ui <- fluidPage(
      actionButton("start", "Trigger layout"), # add the button
      sigmajsOutput("sg")
    )

    server <- function(input, output){

      output$sg <- renderSigmajs({
        sigmajs() %>%
          sg_nodes(nodes, id, size, color) %>%
          sg_edges(edges, id, source, target)
      })

      observeEvent(input$start, {
        sigmajsProxy("sg") %>% # use sigmajsProxy!
          sg_force_start_p() # app the proxy (_p)
      })

    }

    shinyApp(ui, server) # run

So proxies work on a already existing graphs so you simply have to use the `sigmajsProxy` function to catch that graph using its `id`; output graph’s id is `sg` (`sigmajsOutput("sg")`). Then you can pass your proxies `_p`.

We could, for instance, now add another button to kill the layout because as it is now the layout is constantly running which is a bit draining for the browser and not very useful.

    nodes <- sg_make_nodes()
    edges <- sg_make_edges(nodes)

    ui <- fluidPage(
      actionButton("start", "Start layout"), # start button
      actionButton("stop", "Stop layout"), # stop button
      sigmajsOutput("sg")
    )

    server <- function(input, output){

      output$sg <- renderSigmajs({
        sigmajs() %>%
          sg_nodes(nodes, id, size, color) %>%
          sg_edges(edges, id, source, target)
      })

      # start layout
      observeEvent(input$start, {
        sigmajsProxy("sg") %>%
          sg_force_start_p()
      })

      # stop layout
      observeEvent(input$stop, {
        sigmajsProxy("sg") %>%
          sg_force_stop_p()
      })

    }

    shinyApp(ui, server) # run

Now that you are familiar with proxies we can look at the more powerful ones; though you will see, you can use them just as easily! For that we’ll scrap the previous buttons and go back to the basic shiny app we initially set up.

Let’s put a button that lets the user add nodes to the graph. For this example we’ll only plot nodes, no edges.

    library(shiny)
    library(sigmajs)

    # initial nodes
    nodes <- sg_make_nodes()

    # nodes to add on click
    nodes2add <- sg_make_nodes()
    nodes2add$id <- 11:20 # ids must be unique

    ui <- fluidPage(
      actionButton("add", "Add nodes"),
      sigmajsOutput("sg")
    )

    server <- function(input, output){

      output$sg <- renderSigmajs({
        sigmajs() %>%
          sg_nodes(nodes, id, size, color)
      })

      observeEvent(input$add, {
        sigmajsProxy("sg") %>%
          sg_add_nodes_p(nodes2add, id, size, color)
      })
    }

    shinyApp(ui, server) # run

This is a simplified version of the `demo("add-nodes", package = "sigmajs")`

It’s fairly simple when you look at it.

1. We generate additional nodes.
2. We make sure that these additional nodes do not have the same `id` as the already existing nodes.
3. We add them using `sg_add_nodes_p` which acutally works just like `sg_nodes`.

## Events

Another great thing the package lets you do is capture how the user interact with your app. Then again there is a demo for the latter: `custom-events`.

All the events are integrated in the package

Let’s take the basic app we built at the begining of the proxies walkthrough and catch which node the user clicks on.

    library(shiny)
    library(sigmajs)

    nodes <- sg_make_nodes()
    edges <- sg_make_edges(nodes)

    ui <- fluidPage(
      sigmajsOutput("sg"),
      p("Click on a node"),
      verbatimTextOutput("clicked")
    )

    server <- function(input, output){
      output$sg <- renderSigmajs({
        sigmajs() %>%
          sg_nodes(nodes, id, size, color) %>%
          sg_edges(edges, id, source, target)
      })

      # capture node clicked
      output$clicked <- renderPrint({
        input$sg_click_node
      })
    }

    shinyApp(ui, server) # run

Easy! Just use your plot as an `input` that points to the graph id (`sg`) followed by `_` and the name of the event you want to catch; in our case, plot of id (`sg`) and capture node clicked = `input$sg_click_node`. There are many more events to pick up, see the official documentation for the full list.

## Filter

Now that you are familiar with proxies, we can add a filter to filter nodes, edges or both.

- `sg_filter_gt_p` - filter greater than \(x\)
- `sg_filter_lt_p` - filter less than \(x\)
- `sg_filter_eq_p` - filter equal to \(x\)
- `sg_filter_not_eq_p` - filter not equal to \(x\)
- `sg_filter_undo_p` - undo filter
- `sg_filter_neighbours_p` - to filter neighbours of node \(x\)

Let’s take our basic Shiny app and add our filter. Note that we pass a name to the filter, this allows referencing the filter in `sg_filter_undo_p` function. Every time the user moves the slider the filter is actually undone and re-applied.

    nodes <- sg_make_nodes()
    edges <- sg_make_edges(nodes)

    ui <- fluidPage(
      sliderInput(
        "filter",
        "Filter nodes",
        value = 0,
        min = 0,
        max = 5
      ),
      sigmajsOutput("sg")
    )

    server <- function(input, output){

      output$sg <- renderSigmajs({
        sigmajs() %>%
          sg_nodes(nodes, id, size, color) %>%
          sg_edges(edges, id, source, target)
      })

      observeEvent(input$filter, {
        sigmajsProxy("sg") %>%
          sg_filter_undo_p("sz") %>% # we undo the filter before applying it
          sg_filter_gt_p(input$filter, "size", name = "sz")
      })

    }

    shinyApp(ui, server) # run