Compatibility of table formatting with `data.table::rowwiseDT()`

[TimTaylor]

Is it worth adding data.table's rowwiseDT() to your default table set?

[DavisVaughan]

Hmm the empty named arguments would make that difficult

rowwiseDT(
  A=,B=, C=,
  1, "a", 2:3,
  2, "b", list(5)
)
#>        A      B      C
#>    <num> <char> <list>
#> 1:     1      a    2,3
#> 2:     2      b      5

Right now named arguments short circuit the tabling process, i.e. they end the table, which is to support default = in fcase, and in theory makes sense to us because the tabling directive is for laying out unnamed arguments supplied within ....

fcase(
  x < 5L, 1L,
  x > 5L, 3L,
  default = 5L
)

[lionel-]

We also had the idea of aligning names in their own column, but that wouldn't help much here:

rowwiseDT(
  A =   , B =     , C =         ,
      1 ,     "a" ,     2:3     ,
      2 ,     "b" ,     list(5)
)

One thing that could help is a new # fmt: table off directive. You'd use it with trailing named arguments:

fcase(
  x < 5L, 1L,
  x > 5L, 3L,
  # fmt: table off
  default = 5L
)

And then we'd format named arguments normally, aligned according to the type of their RHS, instead of aligned in their own column. If there is no value they'd be left-aligned. You'd get:

rowwiseDT(
  A = , B = , C =     ,
    1 , "a" , 2:3     ,
    2 , "b" , list(5)
)

[lionel-]

We could also allow names in the first row, and still turn off table formatting when we find a name in any ulterior row. That would be justified because disabling table formatting from the first row on (i.e. in the whole table) doesn't make much sense.