R Shiny - Make additional header row of kable table 'sticky'

Question

The kableExtra package has a great function called add_header_above() which creates an additional header row in the output table on top of the actual column names. This can be very useful for grouping data. When setting fixed_thead = TRUE in kable_styling() the actual column names are frozen when scrolling down but this additional header row is not.

Here is a minimal shiny app that shows what I mean. Note that if you view the app in the RStudio viewer neither the normal column header nor the additional ones are sticky. Run it in a proper web browser instead.

library(shiny)
library(magrittr)

ui <- fluidPage(
  tableOutput("table")
)

server <- function(input, output, session) {
  output$table <- function() {
    knitr::kable(mtcars) %>%
      kableExtra::kable_styling(fixed_thead = TRUE) %>%
      kableExtra::add_header_above(c(" " = 1, "Header 1" = 5, "Header 2" = 6))
  }
}

shinyApp(ui, server)

How to make the additional header row created with add_header_above() sticky? I guess I would need to incorporate some CSS or JavaScript in the app to do so.

score 4 · Accepted Answer · answered Mar 04 '20 at 04:05

Inspiration comes from @Stéphane Laurent's answer. Below is a more generic approach for applying the sticky property to any number of headers.

library(shiny)
library(magrittr)

JS <- "
$(document).ready(function() {
  var myInterval = setInterval(function() {
    // clear interval after the table's DOM is available
    if ($('thead').length) {
      clearInterval(myInterval);
    }

    // setting css
    $('thead tr th').css('position', 'sticky').css('background', 'white');

    var height = 0;

    for (var i = 0, length = $('thead tr').length; i < length; i++) {
      var header = $('thead tr:nth-child(' + i + ')');
      height += header.length ? header.height() : 0;
      $('thead tr:nth-child(' + (i + 1) + ') th').css('top', height);
    }

  }, 500);
});
"

ui <- fluidPage(
  tags$head(
    tags$script(HTML(JS))
  ),
  tableOutput("table")
)

server <- function(input, output, session) {
  output$table <- function() {
    knitr::kable(mtcars) %>%
      kableExtra::add_header_above(c(" " = 1, "Header 1" = 5, "Header 2" = 6)) %>%
      kableExtra::add_header_above(c(" " = 1, "Header" = 11)) %>%
      kableExtra::kable_styling()
  }
}

shinyApp(ui, server)

If you don't want your main app.R to have all that Javascript, you can move the code to a different file, see: Include a javascript file in Shiny app.

Good work! I didn't know this technique with `clearInterval`. — Stéphane Laurent, Mar 04 '20 at 17:52

score 2 · Answer 2 · answered Mar 03 '20 at 21:07

library(shiny)
library(magrittr)

CSS <- "
thead tr th {
  position: sticky;
  background-color: white;
}
thead tr:nth-child(1) th {
  top: 0;
}
"

JS <- "
$(document).ready(function(){
  setTimeout(function(){
    var h = $('thead tr:nth-child(1)').height();
    $('thead tr:nth-child(2) th').css('top', h);
  }, 500);
});
"

ui <- fluidPage(
  tags$head(
    tags$style(HTML(CSS)),
    tags$script(HTML(JS))
  ),
  uiOutput("table")
)

server <- function(input, output, session) {
  output$table <- renderUI({
    tabl <- knitr::kable(mtcars) %>%
      kableExtra::add_header_above(c(" " = 1, "Header 1" = 5, "Header 2" = 6)) %>% 
      kableExtra::kable_styling()
    HTML(tabl)
  })
}

shinyApp(ui, server)

R Shiny - Make additional header row of kable table 'sticky'

2 Answers2

Linked