Adding text to a grid.table plot

Question

I have recently started using the grid.table function from the gridExtra package to turn tabular data into png image files for use on the web. I've been delighted with it so far as it produces very good-looking output by default, sort of like a ggplot2 for tables. Like the person who asked this question I would love to see the ability to specify the justification for individual columns but that would be icing on what is an already more-ish cake.

My question is whether it is possible to add text around a grid.table so that I can give plotted tables a title and a footnote. It seems to me this should be feasible, but I don't know enough about grid graphics to be able to work out how to add grobs to the table grob. For example, this code:

require(gridExtra)

mydf <- data.frame(Item = c('Item 1','Item 2','Item 3'), 
　　　　　　　　　　　　　　　　　　　　Value = c(10,15,20), check.names = FALSE)
grid.table(mydf,
           gpar.coretext=gpar(fontsize = 16),
           gpar.coltext = gpar(fontsize = 16),
           gpar.rowtext = gpar(fontsize = 16),
           gpar.corefill = gpar(fill = "blue", alpha = 0.5, col = NA),
           h.even.alpha = 0.5,
           equal.width = FALSE,
           show.rownames = FALSE,
           show.vlines = TRUE,
           padding.h = unit(15, "mm"),
           padding.v = unit(8, "mm")
           )

generates this plot:

enter image description here

when I would really like to be able to do something like the following in code rather than by editing the image with another application:

enter image description here

baptiste · Accepted Answer · 2015-07-16T23:19:50.820

To place text close to the table you'll want to evaluate the table size first,

library(gridExtra)
d <- head(iris)
table <- tableGrob(d)

grid.newpage()
h <- grobHeight(table)
w <- grobWidth(table)
title <- textGrob("Title", y=unit(0.5,"npc") + 0.5*h, 
                  vjust=0, gp=gpar(fontsize=20))
footnote <- textGrob("footnote", 
                     x=unit(0.5,"npc") - 0.5*w,
                     y=unit(0.5,"npc") - 0.5*h, 
                  vjust=1, hjust=0,gp=gpar( fontface="italic"))
gt <- gTree(children=gList(table, title, footnote))
grid.draw(gt)

Edit (17/07/2015) With gridExtra >=2.0.0, this approach is no longer suitable. tableGrob now returns a gtable, which can be more easily customised.

library(gridExtra)
d <- head(iris)
table <- tableGrob(d)

library(grid)
library(gtable)

title <- textGrob("Title",gp=gpar(fontsize=50))
footnote <- textGrob("footnote", x=0, hjust=0,
                     gp=gpar( fontface="italic"))

padding <- unit(0.5,"line")
table <- gtable_add_rows(table, 
                         heights = grobHeight(title) + padding,
                         pos = 0)
table <- gtable_add_rows(table, 
                         heights = grobHeight(footnote)+ padding)
table <- gtable_add_grob(table, list(title, footnote),
                         t=c(1, nrow(table)), l=c(1,2), 
                         r=ncol(table))
grid.newpage()
grid.draw(table)

Thanks, that solves the problem and I learned several things from that. I guess I can also use the table and text grobs in viewports and so on? — SlowLearner, Aug 02 '12 at 13:26
it works, but the color of the table is gone after using this. I can only color to title. — purpleblau, Mar 12 '14 at 16:25

Andrew · Answer 2 · 2015-11-16T15:29:10.320

5

If you want just the title (no footnote), here is a simplified version of @baptiste's example:

title <- textGrob("Title", gp = gpar(fontsize = 50))
padding <- unit(0.5,"line")
table <- gtable_add_rows(
  table, heights = grobHeight(title) + padding, pos = 0
)
table <- gtable_add_grob(
  table, list(title),
  t = 1, l = 1, r = ncol(table)
)
grid.newpage()
grid.draw(table)

edited Nov 16 '15 at 15:29

answered Nov 16 '15 at 15:16

Andrew

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Adding text to a grid.table plot

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