This function detects rows and columns that does not contain any grobs and removes thewm from the gtable. If the rows and/or columns removed had a non-zero height/width the relative layout of the gtable may change.
Examples
library(grid)
rect <- rectGrob(gp = gpar(fill = "black"))
base <- gtable(unit(c(2, 2, 2), "cm"), unit(c(2, 2, 2), "cm"))
center <- gtable_add_grob(base, rect, 2, 2)
plot(center)
plot(gtable_trim(center))
col <- gtable_add_grob(base, rect, 1, 2, 3, 2)
plot(col)
plot(gtable_trim(col))
row <- gtable_add_grob(base, rect, 2, 1, 2, 3)
plot(row)
plot(gtable_trim(row))
