Confusing error with flowchart - inserting single box after a split causes error

[aghaynes]

I tried to add some labels to a flow chart, similar to those in the consort flow (for allocation, followup etc). They're rather headings more than part of the flow itself. I got a confusing error, that doesn't really help resolve anything...

flowchart(
  rando = glue("Randomised N = 100"),
  groups = list(
    glue("Group1\nn = 50"), 
    glue("Group2\nn = 50")
  ),
  groups2 = list(
    glue("Excluded\nn = {1}"), 
    glue("Excluded\nn = {2}")
  ), 
  groups3 = list(
    glue("Analysed\nn = {49}"), 
    glue("Analysed\nn = {48}")
  )
) |> 
  insert(boxGrob("Followup"), 
         after = "groups")

Fehler in coords(prev_box) : 
  Assertion on 'box' failed: Must inherit from class 'box', but has class 'list'.

(in another example using a list of length 1 rather than the boxGrob directly, i got this error: Fehler in coords(next_box) : Assertion on 'box' failed: Must inherit from class 'box', but has classes 'Gmisc_list_of_boxes','list'.

It's fine it I put it above the split groups, but after it, it causes the error, so I assume it's to do with the grouped values.

This is the sort of thing I'm aiming for

[aghaynes]

I figured out a workaround...

fc <- flowchart(
  rando = glue("Randomised N = 100"),
  groups = list(
    glue("Group1\nn = 50"), 
    glue("Group2\nn = 50")
  ),
  groups2 = list(
    glue("Excluded\nn = {1}"), 
    glue("Excluded\nn = {2}")
  ), 
  groups3 = list(
    glue("Analysed\nn = {49}"), 
    glue("Analysed\nn = {48}")
  )
) |> 
  spread(axis = "y") |> 
  spread(subelement = "groups", axis = "x") |> 
  spread(subelement = "groups2", axis = "x") |> 
  spread(subelement = "groups3", axis = "x") 

fc
boxGrob("Allocation", 
        y = fc$groups[[1]]$vp$y + fc$groups[[1]]$vp$height/2, 
        x = .5)
boxGrob("Followup", 
        y = fc$groups2[[1]]$vp$y + fc$groups2[[1]]$vp$height/2, 
        x = .5)
boxGrob("Analysis", 
        y = fc$groups3[[1]]$vp$y + fc$groups3[[1]]$vp$height/2, 
        x = .5)

Maybe that's more flexible than an include-based solution... some sort of accessory function to extract the position might be handy though...
Maybe the error I mentioned originally could still be clearer though...

[gforge]

I think I nailed it:

Checkout version 3.4.0