Using R Shiny's actionButtons to add nodes to a tree

Question

I'm working on a Shiny app where users can start from a table of data, and create new tables based on selected filters/summaries of the previous tables - something like this:

Table1 ---- (filter) > Table2
       ---- (filter) > Table3  ---- (filter) > Table4
                               ---- (filter) > Table5
       ---- (filter) > Table6

Using lists of lists in R, I made a tree data structure (called sliceBox.tree in my code example) to keep track of each table/node. Each table will come with a set of inputs as well: some filter settings and an actionButton, which can be used to create a new child table under that parent table.

I'm using the observeEvent() function to react to each button press, but when I try to append a node to the tree inside the observeEvent handler, the changes are only made to the copy tree inside the function, and the original tree is unaffected. Is there a way to edit the original tree from inside the observeEvent handler or maybe a different approach to do this?

Here is a trimmed-down version of my code now to illustrate the problem - I want the current code to create child actionButtons on the page by clicking on any existing buttons.

server <- function(input, output) {

  newNode <- function(id, parentId) {
    node <- list(
      parent = parentId, 
      children = list(),
      uiObject = createButton(id, parentId) 
    )
    return(node)
  }


  createButton <- function(id, parentId) {
    print(paste0("Creating button ", id))
    buttonID <- paste0("sliceBoxButton", id)
    return(actionButton(buttonID, paste0("I am ", buttonID, ", child of ", parentId), icon("plus-circle fa-2x")))
  }


  rootNode <- newNode(1, 0)
  sliceBox.tree <- list(rootNode) # We'll store our nodes as a 1D list, so parent and child ID's are recorded as their indices in the list
  output$debug <- renderPrint({
    print(paste0("Button presses: ", v$counter))
    print("FULL TREE")
    print(sliceBox.tree)
  })


  # Keep a total count of all the button presses (also used loosely as the number of tables created)
  v <- reactiveValues(counter = 1L) 

  # Event handlers: specific function for particular button will run when that button is pressed
  observeEvent(v$counter, {
    for (id in 1:v$counter) {
      buttonID <- paste0("sliceBoxButton", id)
      observeEvent(input[[buttonID]], {
        v$counter <- v$counter + 1L
        print(paste0("Pressed ", buttonID))


        # Append new child to list of children
        numChildren <- length(sliceBox.tree[[id]]$children)
        sliceBox.tree[[id]]$children[numChildren + 1] <- v$counter 


        sliceBox.tree[[v$counter]] <- newNode(v$counter, id)
        print(paste0("Appending node to tree at index ", v$counter))
        print(sliceBox.tree)
      })
    }
  })


  # renderUI needs a list of uiObjects, so we just extract the uiObjects from every node of the tree
  output$allSliceBoxes <- renderUI({
    table_output_list <- lapply(1:v$counter, function(i) { 
      return(getElement(sliceBox.tree[[i]], 'uiObject'))
    })
    do.call(tagList, table_output_list) # Convert the list to a tagList 
  })


}


ui <- fluidPage(
  uiOutput("allSliceBoxes"),
  verbatimTextOutput('debug')
)


shinyApp(ui = ui, server = server)

Really hope someone can help, I've been googling extensively but haven't found any examples that do something similar - been stuck on this for days!

Mariana Oliveira · Accepted Answer · 2016-08-09 15:51:09Z

1

One way to solve this would be to store your tree in a reactiveValues structure.

# sliceBox.tree <- list(rootNode)
# Use this instead:
sliceBox.tree <- reactiveValues(tree=list(rootNode))

From that point on, change every sliceBox.tree to sliceBox.tree$tree. It works for me.

answered Aug 9, 2016 at 15:51

Mariana Oliveira

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