pre check radio buttons in datatable output in shiny app

Question

I am building a shiny app and I would like the DT table I am using to have pre-checked radio buttons, which then can be changed by the user if necessary. For example in this example: https://yihui.shinyapps.io/DT-radio/, I would like all the months to have pre selected "A", which users can then change to "B" to "E" or just keep "A".

What do I need to change in the code to make that happen?

library(shiny)
library(DT)
shinyApp(
  ui = fluidPage(
    title = 'Radio buttons in a table',
    DT::dataTableOutput('foo'),
    verbatimTextOutput('sel')
  ),
  server = function(input, output, session) {
    m = matrix(
      as.character(1:5), nrow = 12, ncol = 5, byrow = TRUE,
      dimnames = list(month.abb, LETTERS[1:5])
    )
    for (i in seq_len(nrow(m))) {
      m[i, ] = sprintf(
        '<input type="radio" name="%s" value="%s"/>',
        month.abb[i], m[i, ]
      )
    }
    m
    output$foo = DT::renderDataTable(
      m, escape = FALSE, selection = 'none', server = FALSE,
      options = list(dom = 't', paging = FALSE, ordering = FALSE),
      callback = JS("table.rows().every(function(i, tab, row) {
          var $this = $(this.node());
          $this.attr('id', this.data()[0]);
          $this.addClass('shiny-input-radiogroup');
        });
        Shiny.unbindAll(table.table().node());
        Shiny.bindAll(table.table().node());")
    )
    output$sel = renderPrint({
      str(sapply(month.abb, function(i) input[[i]]))
    })
  }
)

Answer 1

You have to add the checked attribute in the first column:

for (i in seq_len(nrow(m))) {
  m[i, 1] = sprintf(
    '<input type="radio" name="%s" value="%s" checked/>',
    month.abb[i], m[i, 1]
  )
  m[i, 2:5] = sprintf(
    '<input type="radio" name="%s" value="%s"/>',
    month.abb[i], m[i, 2:5]
  )
}