DT Shiny different custom column header by column

Question

my css skills are extremely limited but assuming the following example:

  sketch = htmltools::withTags(table(
     class = 'display',
     thead(
        tr(
           th(rowspan = 2, 'Species'),
           th(colspan = 2, 'Sepal'),
           th(colspan = 2, 'Petal')
        ),
        tr(
           lapply(rep(c('Length', 'Width'), 2), th)
        )
     )
  ))
  datatable(head(iris, 10), 
     container = sketch, options = list(
     initComplete = JS(
        "function(settings, json) {",
        "$(this.api().table().header()).css({'background-color': '#000', 'color': '#fff'});",
        "}")
  ))

How would I change the color coding of the first two column headers into say blue so that both rows of the column header Sepal,Length and Sepal,Width are blue, but retaining as another color the following structure Petal,Length and Petal,Width

After Stephane's initial answer, I added an example.

Protozoology

Answer 1

You can use the option headerCallback.

datatable(head(iris, 10), 
          container = sketch, options = list(
            headerCallback = JS(
              "function( thead, data, start, end, display ) {
      $(thead).closest('thead').find('th').eq(3).css('color', 'red');
      $(thead).closest('thead').find('th').eq(4).css('color', 'red');
      $(thead).closest('thead').find('th').eq(5).css('color', 'blue');
      $(thead).closest('thead').find('th').eq(6).css('color', 'blue');
              }"
            ),
            initComplete = JS(
              "function(settings, json) {",
              "$(this.api().table().header()).css({'background-color': '#000', 'color': '#fff'});",
              "}")
          ))

The .closest('thead') is needed when the header has multiple rows.

Is it what you want? I'm not sure I have correctly understood your request.

---

To change the background color:

library(DT)

sketch = htmltools::withTags(table(
  class = 'display',
  thead(
    tr(
      th(rowspan = 2, 'Species'),
      th(colspan = 2, 'Sepal'),
      th(colspan = 2, 'Petal')
    ),
    tr(
      lapply(rep(c('Length', 'Width'), 2), th)
    )
  )
))

headerCallback <- "function( thead, data, start, end, display ) {
  $(thead).closest('thead').find('th').eq(0).css('background-color', 'green');
  $(thead).closest('thead').find('th').eq(1).css('background-color', 'red');
  $(thead).closest('thead').find('th').eq(2).css('background-color', 'blue');
  $(thead).closest('thead').find('th').eq(3).css('background-color', 'red');
  $(thead).closest('thead').find('th').eq(4).css('background-color', 'red');
  $(thead).closest('thead').find('th').eq(5).css('background-color', 'blue');
  $(thead).closest('thead').find('th').eq(6).css('background-color', 'blue');
}"

datatable(head(iris, 10), 
          container = sketch, options = list(
            headerCallback = JS(headerCallback)
          )
)

Carpentry

Stephane thank you! I'm sure your initial answer will not go to waste in the future - please see example added - the plan is to make it easy for users to discriminate column structures not by the font color but by the background color. Hope that makes sense. – Protozoology

@J.Doe. You're welcome. I've just edited my answer to show how to change the background color. – Hyden