Christopher Peralta
Reputation: 431
How can I store grobs in a list and pass them to grobTree()?
So I'm trying to make a list of grobs and then pass them into grobTree(), but my list items don't get read in as grobs by do.call().
Here's my code:
library(purrr)
library(grid)
library(gridExtra)
library(ggplot2)
qplot(displ, year, data = mpg)
title_segments <- c('Help ', 'me ', 'please', '!')
colors <- c('red', 'orange', 'green', 'blue')
nudge_x = 0
grobs <- NULL
grobs[1] <- list(gp = gpar(fontsize = 14, fontface = 'bold'))
grobs[2] <- list(textGrob(label = title_segments[1], name = "title1",
x = unit(2.33 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[1])))
if(length(title_segments) > 1){
x <- unit(2.24 - nudge_x, "lines")
more_grobs <- pmap(list(title_segments[-1], colors[-1],
seq_along(title_segments)[-1]), function(segment, color, i){
grob <- textGrob(label = segment, name = paste0('title', i, sep = ''),
x = x + grobWidth(paste0('title', i - 1, sep = '')),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = color))
})
}
grobs <- c(grobs, more_grobs)
grobs <- do.call(what = grobTree, args = grobs) ### ERROR HERE
# Turn off clipping and draw plot
gb <- ggplot_build(last_plot())
gt <- ggplot_gtable(gb)
gt$layout$clip[gt$layout$name=="panel"] <- "off"
gg <- arrangeGrob(gt, top = grobs, padding = unit(2.6, "line"))
grid.newpage()
grid.draw(gg)
The error occurs when I get to the do.call() statement, because my list elements don't get read as grobs.
When I try this bit of code, then it evaluates to true.
var <- NULL
is.grob(var <- textGrob(label = title_segments[1], name = "title1",
x = unit(2.33 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[1])))
When I try this bit, it evaluates to false
var2 <-NULL
var2[1] <- textGrob(label = title_segments[1], name = "title1",
x = unit(2.33 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[1])))
is.grob(var2[1])
EDIT:: This is what I'm trying to achieve with the pmap function.
grobs <- grobTree(
gp = gpar(fontsize = 14, fontface = 'bold'),
textGrob(label = title_segments[1], name = "title1",
x = unit(2.33 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[1])),
if(length(title_segments) > 1){
textGrob(label = title_segments[2], name = "title2",
x = grobWidth("title1") + unit(2.24 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[2]))
},
if(length(title_segments) > 2){
textGrob(label = title_segments[3], name = "title3",
x = grobWidth("title1") + grobWidth("title2") + unit(2.24 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[3]))
},
if(length(title_segments) > 3){
textGrob(label = title_segments[4], name = "title4",
x = grobWidth("title1") + grobWidth("title2") + grobWidth("title3") + unit(2.24 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[4]))
},
if(length(title_segments) > 4){
textGrob(label = title_segments[5], name = "title5",
x = grobWidth("title1") + grobWidth("title2") + grobWidth("title3") + grobWidth("title4") + unit(2.24 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[5]))
}
)
Upvotes: 5
Views: 1215
Answers (1)
Claus Wilke
Reputation: 17810
Let's attempt to answer the question as written. The question as I read it goes as follows:
This code works:
grobs <- grobTree(
gp = gpar(fontsize = 14, fontface = 'bold'),
textGrob(label = title_segments[1], name = "title1",
x = unit(2.33 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[1])),
if(length(title_segments) > 1){
textGrob(label = title_segments[2], name = "title2",
x = grobWidth("title1") + unit(2.24 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[2]))
},
if(length(title_segments) > 2){
textGrob(label = title_segments[3], name = "title3",
x = grobWidth("title1") + grobWidth("title2") + unit(2.24 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[3]))
},
if(length(title_segments) > 3){
textGrob(label = title_segments[4], name = "title4",
x = grobWidth("title1") + grobWidth("title2") + grobWidth("title3") + unit(2.24 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[4]))
},
if(length(title_segments) > 4){
textGrob(label = title_segments[5], name = "title5",
x = grobWidth("title1") + grobWidth("title2") + grobWidth("title3") + grobWidth("title4") + unit(2.24 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[5]))
}
)
However, this code, which is meant as a computational recreation of the previous code, does not:
grobs <- NULL
grobs[1] <- list(gp = gpar(fontsize = 14, fontface = 'bold'))
grobs[2] <- list(textGrob(label = title_segments[1], name = "title1",
x = unit(2.33 - nudge_x, "lines"),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = colors[1])))
if(length(title_segments) > 1){
x <- unit(2.24 - nudge_x, "lines")
more_grobs <- pmap(list(title_segments[-1], colors[-1],
seq_along(title_segments)[-1]), function(segment, color, i){
grob <- textGrob(label = segment, name = paste0('title', i, sep = ''),
x = x + grobWidth(paste0('title', i - 1, sep = '')),
y = unit(-.5, "lines"),
hjust = 0, vjust = 0, gp = gpar(col = color))
})
}
grobs <- c(grobs, more_grobs)
grobs <- do.call(what = grobTree, args = grobs) ### ERROR HERE
What's going on? The answer is that the problem lies in the first two lines:
grobs <- NULL
grobs[1] <- list(gp = gpar(fontsize = 14, fontface = 'bold'))
The assignment grobs[1] <- removes the naming of gp = ... for the list element, and therefore the function grobTree() doesn't understand that the first argument is not a grob. The fix is simple. Replace those two lines with:
grobs <- list(gp = gpar(fontsize = 14, fontface = 'bold'))
Now things work, sort of. The do.call() line does not cause an error anymore. However, the spacing of the words is still not right, because the pmap() call doesn't create a sum of all the grob widths from the first to the nth. Instead it only uses the grob width of the previous grob. This problem is best solved with a recursive function, I think:
make_grobs <- function(words, colors, x, y, hjust = 0, vjust = 0, i = 0) {
n <- length(words)
colors <- rep_len(colors, n)
name <- paste0('title', i)
grob <- textGrob(label = words[1], name = name,
x = x, y = y, hjust = hjust, vjust = vjust,
gp = gpar(col = colors[1]))
if (n == 1) {
list(grob)
}
else {
c(list(grob),
make_grobs(words[-1], colors[-1],
x + grobWidth(grob), y, hjust, vjust, i + 1))
}
}
With this function defined, the entire reproducible example becomes:
library(purrr)
library(grid)
library(gridExtra)
library(ggplot2)
title_segments <- c('Help ', 'me ', 'please', '!')
colors <- c('red', 'orange', 'green', 'blue')
nudge_x = 0
grobs <- do.call(what = grobTree,
args = c(make_grobs(title_segments, colors,
x = unit(2.33 - nudge_x, "lines"),
y = unit(-.5, "lines")),
list(gp = gpar(fontsize = 14, fontface = 'bold'))))
qplot(displ, year, data = mpg)
gb <- ggplot_build(last_plot())
gt <- ggplot_gtable(gb)
gt$layout$clip[gt$layout$name=="panel"] <- "off"
gg <- arrangeGrob(gt, top = grobs, padding = unit(2.6, "line"))
grid.newpage()
grid.draw(gg)
Upvotes: 3
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