Assume that I have a reactive which returns a data.frame. I want some of my controls to take a dependency only on a subset of its columns, that is it should only fire, if values in any of the “relevant” columns (here rel_1 and rel_2) change, while changes in the “irrelevant” columns (here irr_1and irr_2) should not trigger a refresh.

I thought creating a reactive which returns only the relevant columns should do the trick, but the following code shows that all the buttons trigger a refresh of the verbatimTextOutput. My expectation would be that a press to Change Irrelevant Columns would not trigger a refresh, because the values in the relevant columns remain unchanged.

library(shiny)
library(DT)
library(dplyr)
library(glue)

dat <- tibble(
  rel_1 = LETTERS[1:3],
  rel_2 = letters[1:3],
  irr_1 = 1:3,
  irr_2 = 101:103
)

ui <- fluidPage(
  fluidRow(
    column(
      width = 4,
      actionButton("chng_all", "Change All Columns")
    ),
    column(
      width = 4,
      actionButton("chng_irr", "Change Irrelevant Columns")
    ),
    column(
      width = 4,
      actionButton("chng_rel", "Change Relevant Columns")
    )
  ),
  fluidRow(
    column(
      width = 12,
      DTOutput("tbl")
    )    
  ),
  fluidRow(
    column(
      width = 12,
      verbatimTextOutput("dbg")
    )    
  )
)

server <- function(input, output, session) {
  my_data <- reactiveVal(dat)
  
  change_values <- function(data, cols) {
    data %>% 
      mutate(
        across(all_of(cols),
               ~ if (is.numeric(.x)) sample(100, 3) else sample(LETTERS, 3))
      )
  }
  
  relevant_data <- reactive(
    my_data() %>% 
      select(starts_with("rel"))
  )
  
  observe({
    my_data(change_values(my_data(), c(paste0("irr_", 1:2),
                                       paste0("rel_", 1:2))))
  }) %>% 
    bindEvent(input$chng_all)
  
  observe({
    my_data(change_values(my_data(), paste0("irr_", 1:2)))
  }) %>% 
    bindEvent(input$chng_irr)
  
  observe({
    my_data(change_values(my_data(), paste0("rel_", 1:2)))
  }) %>% 
    bindEvent(input$chng_rel)
  
  output$tbl <- renderDT(
    datatable(my_data())
  )
  
  output$dbg <- renderPrint({
    glue("Relevant Data Last Changed: {Sys.time()}")
  }) %>% 
    bindEvent(relevant_data())
  
}

shinyApp(ui, server)