R Shiny: Creating New Columns Within a Reactive Data Frame

Question

Say I have a data frame called summarized which includes the columns TY_COMP and LY_COMP (among others). I could write a function in R that performs a calculation on TY_COMP and LY_COMP and creates a new column called cac in the data frame like this:

summarized$cac <- summarized$TY_COMP/summarized$LY_COMP-1

cac is now a new column in the summarized data frame.

Now say that summarized() is a reactive data frame with the same columns.

How could I achieve the effect done in the non-reactive data frame, i.e. create a new column within the current frame? Or how would I get the same effect?

I tried:

summarized$cac <- reactive({summarized()$TY_COMP/summarized()$LY_COMP-1})

Answer 1

I reckon you want to modify a reactive when for example an actionButton is clicked. For this purpose I would use reactiveValues. You can modify reactiveValue inside of observers such as observe or observeEvent.

Check out this simple example:

summarized <- data.frame(id = 1:20, group = letters[1:4], TY_COMP = runif(20), LY_COMP = runif(20))

library(shiny)

ui <- fluidPage(
  verbatimTextOutput("text"),
  actionButton("btn", "Add the 'cac' column to summarized")
)

server <- function(input, output){
  rv <- reactiveValues(summarized = summarized)

  output$text <- renderPrint(rv$summarized)

  observeEvent(input$btn, {
    rv$summarized$cac <- summarized$TY_COMP / summarized$LY_COMP - 1
  })

  summarized_mod <- reactive({
    summarized()$TY_COMP / summarized()$LY_COMP-1
  })
}

shinyApp(ui, server)

Another option would be to create another reactive that has an additional column. This is possible to use, but depending on your use case, I recommend the first solution.

Example:

summarized <- data.frame(id = 1:20, group = letters[1:4], TY_COMP = runif(20), LY_COMP = runif(20))

library(shiny)

ui <- fluidPage(
  verbatimTextOutput("text1"),
  verbatimTextOutput("text2")
)

server <- function(input, output){

  output$text1 <- renderPrint(summarized_orig())
  output$text2 <- renderPrint(summarized_mod())


  summarized_orig <- reactive( {
    summarized
  })

  summarized_mod <- reactive({
    df <- summarized_orig()
    df$cac <- summarized_orig()$TY_COMP / summarized_orig()$LY_COMP - 1

    df
  })
}

shinyApp(ui, server)