gridExtra Colour different rows with tableGrob

Question

I have a question regarding tableGrob/grid.table from the gridExtra package. Using the regular parameter settings, it is straightforward to colour alternate rows. However,

Answer 1

starting with v>=2.0.0 of gridExtra, grid.table is now based on gtable, and can be customised to deeper levels than in previous versions. The vignette has more examples, but for completeness here is an example illustrating how to highlight specific cells,

g <- tableGrob(iris[1:4, 1:3])
find_cell <- function(table, row, col, name="core-fg"){
  l <- table$layout
  which(l$t==row & l$l==col & l$name==name)
}

ind <- find_cell(g, 3, 2, "core-fg")
ind2 <- find_cell(g, 2, 3, "core-bg")
g$grobs[ind][[1]][["gp"]] <- gpar(fontsize=15, fontface="bold")
g$grobs[ind2][[1]][["gp"]] <- gpar(fill="darkolivegreen1", col = "darkolivegreen4", lwd=5)
grid.draw(g)

Edit: the above function is easily "vectorised"

find_cells <- function(table, row, col, name="core-fg"){
  l <- table$layout
  unlist(Map(function(r, c) which(((l$t-1) == r) & ((l$l-1) == c) & (l$name == name)), row, col))
}

modify_cells <- function(g, ids, gp=gpar()){
  for(id in ids) g$grobs[id][[1]][["gp"]] <- gp
  return(g)
}

ids <- find_cells(g, 1:3, c(3,2, 1), "core-fg")
g <- modify_cells(g, ids, gpar(fontsize=15, fontface="bold"))

grid.newpage()
grid.draw(g)

Note that in most cases it would make more sense to specify the parameters during the table construction,

faces <- sample(1:4, size = prod(dim(iris[1:4, 1:2])), replace = TRUE)
tt <- ttheme_default(core=list(fg_params=list(fontface=faces)))

grid.table(iris[1:4, 1:2], theme=tt)