grid = grid() not working properly with faceted plots

[grantmcdermott]

Specifically, it only seems to be working for the first facet. Tweaked example from the README, where we use grid = grid() instead of grid = TRUE.

library(tinyplot)
plt(
  Sepal.Length ~ Petal.Length | Sepal.Length, data = iris,
  facet = ~Species, facet.args = list(bg = "grey90"),
  pch = 19,
  main = "Faceted Species!",
  grid = grid(), # <--
  frame = FALSE
)

^{Created on 2024-08-04 with reprex v2.1.1}

[vincentarelbundock]

Not 100%, but there's a chance this is my fault.

The grid argument must be passed explicitly to the helper functions I have modularized. When they are passed via ... it gets evaluated at an undesirable time.

[grantmcdermott]

Thanks, don't stress. It's not a major bug (and may well have been there for ages). But still worth fixing when we get a sec.

[grantmcdermott]

I looked into this as part of #207, but it was trickier to fix than I had time for.

The problem is here...

tinyplot/R/facet.R

Line 396 in e5ac2b6

if (is.null(grid)) grid = .tpar[["grid"]]

... since grid gets evaluated during the is.null() check, which in turn ends up (re)assigning the values of the grid argument to a list of atx and aty values (as per grid). So, we're basically dealing with some unhelpful combination of NSE, promises, and argument/function overloading.

I tried various things, including using !exists("grid") instead of is.null(grid), as well as deparse1(substitute(grid)), but I couldn't get it to work.

Maybe someone else wants to take a stab?

[zeileis]

I don't think that there is a "good" workaround which we could apply only in the draw_facet_window() function. If there is, it would probably be rather fragile. Hence, I see two routes which we could consider - but I haven't thought them through! I just wanted to mention them here in case it is helpful for the discussion. If not, that's also ok.

• substitute() earlier.
  This would be similar to what we do for palette= and legend= for which we just substitute() (without deparse()) early on in tinyplot.default() and then later on essentially do eval(str2lang(...), ...) in the auxiliary functions.
• Introduce a helper function like tinygrid().
  Then we could make tinygrid() a function that processes its arguments and returns a function $grid() (among other elements if needed) that we can then evaluate later on.