R Shiny: Creating New Columns Within a Reactive Data Frame - r

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)