In R/Shiny, how do I trigger an Observe Event using an action button?

Question

This is a simplified and clearer version of my previous post "In R/Shiny, how do I use Action Button to trigger Observe Event function?"

The below code outputs a plot of user inputs, on a Reactive basis, so the user can watch his build of inputs. The plot needs to remain reactive (not linked to the click of the Action Button). The Observe Event in the below code creates an R object out of those inputs (called "matrix_inputs.R"), for use in another R function not shown here. I would like to have the user save that input data into the R object (trigger the Observe Event) only when the user clicks the Action Button. The user could then continue inputting more data into the input matrix and watch the plot change on a reactive basis, without changing that R object. If the user clicks the action button again after making these further changes, that updated data would then be saved and written over that same R object created in Observe Event.

I understand I should insert "input$go, {...}" into the Observe Event. It´s not in the below code because the App will not work if I insert it, it immediately crashes. I have tried various iterations with no luck. Anyone have any insights on how to make this work? Keeping the plot completely real-time reactive, while linking the Observe Event to the Action Button.

Here´s the code:

library(shiny)
library(shinyMatrix)

m <- matrix(c(1,1), 1, 2, dimnames = list(NULL, c("Y", "Z"))) 

ui <- fluidPage(   
  
  titlePanel("Vector Generator"),   
  
  sidebarPanel(
    width = 6,     
    tags$h5(strong("Matrix inputs:")),     
    matrixInput("matrix_input",
                value = m,
                rows = list(extend = TRUE, names = TRUE, editableNames = TRUE),
                cols = list(extend = FALSE, names = TRUE, editableNames = FALSE),
                class = "numeric")
  ), # closes sidebarPanel
  
  actionButton(inputId = "go",label = "Save data"),
  
  mainPanel(
    
    h5(strong("Plot of matrix inputs:")),
    width = 6,plotOutput("graph"),
    
    h5(strong("Table of matrix inputs:")),
    tableOutput("view"),
  
  ) # closes main panel
)   # closes user input (UI) section

server <- function(input, output, session) {   
  
  matrix_input <- reactive(input$matrix_input)

  # Captures input data for further processing in R ----
  observeEvent(matrix_input(), {matrix_input.R <<- unique(matrix_input())})
  
  output$graph <- renderPlot({     
    plot(matrix_input(),type="b")
  }) 
  
  output$view <- renderTable({
    matrix_input()
  })
  
} # closes user server section

shinyApp(ui, server)

Matt Kaye Matt Kaye · Accepted Answer · 2021-05-28T18:24:40

Assuming I'm understanding you right and you want to render the plot when the user presses "Go", I'd just try this for your server instead:


server <- function(input, output, session) {   
  
  matrix_input <- reactive(input$matrix_input)

  # Captures input data for further processing in R ----
  
  observeEvent(input$go, {
   matrix_input.R <<- unique(matrix_input)
  }

  output$graph <- renderPlot({     
    plot(matrix_input(),type="b")
  }) 
  
  output$view <- renderTable({
    matrix_input()
  })
} # closes user server section

That should run the plots when the user presses "go" but not before

In R/Shiny, how do I trigger an Observe Event using an action button?

1 Answers