Merge cells horizontally with datatable in R

I would like to merge cells horizontally (merge 2 columns) on one row.

Minimum, reproducible example:

datatable(data.frame('A' = c('a', 1),'B' = c('bc', 2),'C' = c('', 3),'D' = c('de', 4),'E' = c('', 5)))

Desired output:

Thank you!