R reactable Grouped Columns programaticaly

Question

I have this dataset in R. I'd like to transform it with R package reacatable.

dt <-
  data.table(
    month = seq(1, 12),
    aa_2019 = seq(1, 12),
    bb_2019 = seq(1, 12),
    
    aa_2020 = seq(1, 12),
    bb_2020 = seq(1, 12),
    
    aa_2021 = seq(1, 12),
    bb_2021 = seq(1, 12),
    
    aa_2022 = seq(1, 12),
    bb_2022 = seq(1, 12)
)

Desired output looks like this. Is there a way how to make it automatically? Imagine having sequence of years from 1900 to 2023.

reactable(
  dt,
  columns = list(
    aa_2019 = colDef(name = "aa"),
    bb_2019 = colDef(name = "bb"),
    
    aa_2020 = colDef(name = "aa"),
    bb_2020 = colDef(name = "bb"),
    
    aa_2021 = colDef(name = "aa"),
    bb_2021 = colDef(name = "bb"),
    
    aa_2022 = colDef(name = "aa"),
    bb_2022 = colDef(name = "bb")
  ),
  columnGroups = list(
    colGroup(name = "2019", columns = c("aa_2019", "bb_2019")),
    colGroup(name = "2020", columns = c("aa_2020", "bb_2020")),
    colGroup(name = "2021", columns = c("aa_2021", "bb_2021")),
    colGroup(name = "2022", columns = c("aa_2022", "bb_2022"))
  )
)

Answer 1

Here is one approach to create your colDefs and colGroups dynamically:

library(reactable)

cols <- names(dt)[-1]
cols_split <- strsplit(cols, "_")

cols <- data.frame(
  name = cols,
  group = sapply(cols_split, `[[`, 1),
  year = sapply(cols_split, `[[`, 2)
)

col_defs <- lapply(
  cols$group,
  \(x) {
    colDef(name = x)
  }
) |>
  setNames(cols$name)

col_groups <- cols |>
  split(~year) |>
  lapply(\(x) {
    colGroup(name = unique(x$year), columns = x$name)
  }) |> 
  unname()

reactable(
  dt,
  columns = col_defs,
  columnGroups = col_groups
)