Feature request: Add colspans for grouping headers

[billdenney]

I have a table where the grouping headers are long. So, it would be helpful if they spanned across multiple columns of output (I think using the flextable::merge_at() function).

I can provide a reprex soon. (I'm currently working on a report where I am trying to make this happen...)

[benjaminrich]

Yes, please give me an example.

[billdenney]

Here is the example:

library(table1)
d <- data.frame(A = 1:10, B = 11:20)
label(d$A) <- "Anything really long will illustrate the point here"
table1(~A, data = d)

Which yields the following table:

My thought is to have the heading "Anything really long..." colspan into the result columns so that the table itself can be narrower. I will try to make a patch to also accomplish the goal.

[benjaminrich]

Please have a look at #36.

[billdenney]

I'm working in a .PDF, so I don't think that a JavaScript solution would help (since it's not .html).

The PR that I made should work anywhere t1flex works. If you'd like, I can make a less invasive PR with just the required changes (many of the changes related to me trying to find the right part to change).

[benjaminrich]

In that case I need to think about it.

[benjaminrich]

The problem for me is that this is a really special case. I don't want to add an additional argument and a bunch of code just to handle a special case. This should be handled outside the package in my opinion. You already seem to know how to do that. Another way would be like this:

rndr <- function(x, name, ...) {
    r <- render.default(x, ...)
    r[1] <- label(d[[name]])
    r
}

table1(~A, data = d, render = rndr) |> t1flex() |>
    flextable::merge_h() |>
    flextable::set_table_properties(layout = "autofit")

(I tried it in a PDF and it worked)

[billdenney]

I apologize for the invasive PR that I made first. I should have made a minimal one.

The new PR #135 shows the minimal way to make the changes. That new PR would be a breaking change since it always has the labels span all columns without a new argument. I'm happy to make it into a non-breaking change by adding the function argument, if desired, but I wanted to illustrate the minimal need first.

The suggested code does not accomplish the goal because flextable::merge_h() requires all values within a row to be the same to perform the merge. The first changed line in #135 (https://github.com/benjaminrich/table1/pull/135/files#diff-eb9ff74cf8a7929e803c1a38c97e1c10a17f09889596f2b6f7b431f088d2b2a4R1248) is required to make merge_h() work by making all values in the label row the same. I don't know of a foolproof way to make all values in a row the same after the table has been rendered (i.e. after the call to t1flex()).

Here is a reprex for what I'm looking to change (the spans on the first row needs to be 2 in this case):

library(table1)
#> 
#> Attaching package: 'table1'
#> The following objects are masked from 'package:base':
#> 
#>     units, units<-
d <- data.frame(A = 1:10, B = 11:20)
label(d$A) <- "Anything really long will illustrate the point here"

merged_h <-
  table1(~A, data = d) |>
  t1flex() |>
  flextable::merge_h()
#merged_h
merged_h$body$spans$rows
#>      [,1] [,2]
#> [1,]    1    1
#> [2,]    1    1
#> [3,]    1    1

^{Created on 2025-05-12 with reprex v2.1.1}