the filter & server mode now play nicely with the colReorder extension

[shrektan]

Closes #531

Description

Before this PR, if the user enables the colReorder extension, the filter will return wrong results in the client mode. In the server processing mode, the table will be reverted to the original order whenever it gets re-drawed (i.e., triggered by the filter, search or the paginate button)

The causes

• Client Mode: The row data returned by the datatable is reordered but the filter functions itself is bind to the original order. So the wrong data gets filtered;
• Server Mode: Since the data processing is done in R, the row data is not reordered. However, because R doesn't know the columns have been reordered, it returns the data with column unchanged.

After this PR

It should work for both cases.

The example

library(shiny)
library(DT)

ui <- fluidPage(
  h1("server - FALSE"),
  fluidRow(
    column(
      6,
      DT::dataTableOutput('tbl_with_colreorder')
    ),
    column(
      6,
      DT::dataTableOutput('tbl_wo_colreorder')
    )
  ),
  h1("server - TRUE"),
  fluidRow(
    column(
      6,
      DT::dataTableOutput('tbl_with_colreorder_s')
    ),
    column(
      6,
      DT::dataTableOutput('tbl_wo_colreorder_s')
    )
  )
)

server <- function(input, output, session) {
  output$tbl_with_colreorder = DT::renderDataTable(
    iris, server = FALSE,
    filter = "top", 
    caption = 'with ColReorder',
    extensions = 'ColReorder',
    options = list(colReorder = TRUE)
  )
  output$tbl_wo_colreorder = DT::renderDataTable(
    iris, server = FALSE,
    filter = "top", 
    caption = 'w/o ColReorder'
  )
  output$tbl_with_colreorder_s = DT::renderDataTable(
    iris, server = TRUE,
    filter = "top", 
    caption = 'with ColReorder',
    extensions = 'ColReorder',
    options = list(colReorder = TRUE)
  )
  output$tbl_wo_colreorder_s = DT::renderDataTable(
    iris, server = TRUE,
    filter = "top", 
    caption = 'w/o ColReorder'
  )
}

runApp(shinyApp(ui, server))

[yihui]

This is great! Thanks!

[yihui]

Does it have to be a function? I mean, does this work?

var colReorderEnabled = "colReorder" in options;

[shrektan]

Actually, I used the non-function version at first and worked fine...

However, I overthinked that the options may get changed somewhere else after the table being initialized... It's OK to change it.

[yihui]

I see. It should not matter much. I'm fine to use a function here.

[yihui]

I wonder if there is a way to reorder the data on the server side. If there is, the implementation could be much easier (data[order] in R instead of a nested loop in JS). Of course, it depends on whether we have the order information on the server side.

[shrektan]

Yes, but the datatables library doesn't send the reordered column info to the server by default. We need to register a callback in the event column-reorder, which sends the info to the R side. If this method is better, I guess it's not very difficult to make the change.

[yihui]

In that case, let's just forget it. I'm not too concerned about the performance of the nested loops here since data should typically be small enough.

[shrektan]

I had the concern too... For the deep copy and nested loops... but as you said, it should be fine in the most cases.

[yihui]

Just a reminder to myself -- I need to update the docs at https://rstudio.github.io/DT/extensions.html