Highlight DT diagonal in R Shiny

Question

I have a large datatable in a Shiny app and would like to highlight the diagonal, using logic something like if rowNum == colNum then 'blue' else 'white'.

The rowCallback DT option would let me style by row number, but I can't find anything in the docs that would do the equivalent for column number at the same time.

The best idea I have is to create ~200 extra boolean columns in the table just to determine whether each cell is highlighted or not, hiding them, and using formatStyle(valueColumns = 201:400) to style the others. But that seems like massive overkill here. Any bright ideas?

user_16853114 · Answer

library(tidyverse)
library(DT)
data <- rbind(c(1,2,3), c(4,5,6), c(7,8,9)) %>% as_tibble()
data
#> # A tibble: 3 x 3
#>      V1    V2    V3
#>     
#> 1     1     2     3
#> 2     4     5     6
#> 3     7     8     9
data <-
  data %>%
  mutate(row_id = row_number()) %>%
  pivot_longer(-row_id) %>%
  group_by(row_id) %>%
  mutate(
    col_id = row_number(),
    value = value %>% as.character(),
    value = case_when(
      row_id == col_id ~ str_glue(" {value} "),
      TRUE ~ value
    )
  ) %>%
  ungroup() %>%
  select(row_id, name, value) %>%
  pivot_wider() %>%
  select(-row_id)
data
#> # A tibble: 3 x 3
#>   V1                         V2                        V3                       
#>                                                               
#> 1 … 2                         3                        
#> 2 4                           3 7                          8

user_1100107 · Answer

@danloo's answer gives the desired rendering but you should avoid HTML in cells, because it disturbs the sorting. Here is a way with rowCallback:

library(DT)

js <- c(
  "function(row, data, displayNum, displayIndex, dataIndex){",
  "  $('td:eq(' + dataIndex + ')', row).css('background-color', 'yellow');",
  "}"
)

dat <- as.data.frame(matrix(1:9, nrow = 3))

datatable(
  dat,
  rownames = FALSE, 
  options = list(
    rowCallback = JS(js)
  )
)

Highlight DT diagonal in R Shiny

2 Answers