Printing multiple ggplots into a single pdf, multi

Question

I have a list, p, where each element of p is a list of ggplot2 plotting objects.

I would like to output a single pdf containing all the plots in p such that the plots in p[[1]] are on page 1, the plots in p[[2]] are on page 2, etc. How might I do this?

Here's some example code to provide you with the data structure I'm working with--apologies for the boring plots, I picked variables at random.

require(ggplot2)
p <- list()

cuts <- unique(diamonds$cut)
for(i in 1:length(cuts)){
    p[[i]] <- list()
    dat <- subset(diamonds, cut==cuts[i])
    p[[i]][[1]] <- ggplot(dat, aes(price,table)) + geom_point() + 
        opts(title=cuts[i])
    p[[i]][[2]] <- ggplot(dat, aes(price,depth)) + geom_point() + 
        opts(title=cuts[i])
}

Answer 1

Here is a simpler version of Sven's solution for the R beginners who would otherwise blindly use the do.call and nested lists that they neither need nor understand. I have empirical evidence. :)

library(ggplot2)
library(gridExtra)

pdf("plots.pdf", onefile = TRUE)
cuts <- unique(diamonds$cut)
for(i in 1:length(cuts)){
    dat <- subset(diamonds, cut==cuts[i])
    top.plot <- ggplot(dat, aes(price,table)) + geom_point() + 
        opts(title=cuts[i])
    bottom.plot <- ggplot(dat, aes(price,depth)) + geom_point() + 
        opts(title=cuts[i])
    grid.arrange(top.plot, bottom.plot)
}
dev.off()

Answer 2

Here's one solution, but I don't particularly like it:

ggsave("test.pdf", do.call("marrangeGrob", c(unlist(p,recursive=FALSE),nrow=2,ncol=1)))

The problem is that it relies on there being the same number of plots in each group. If all(sapply(p, length) == 2) were false, then it would break.

Answer 3

I've tried some of these solutions but with no success. I researched a little more and found a solution that worked perfectly for me. It saves all my graphics in a single pdf file, each chart on one page.

library(ggplot2)


pdf("allplots.pdf",onefile = TRUE)
for(i in glist){
   tplot <- ggplot(df, aes(x = as.factor(class), y = value))
   print(tplot)
}
dev.off()

Answer 4

Here's a function based on Sven's approach, including the roxygen2 documentation and an example.

#' Save list of ggplot2 objects to single pdf
#'
#' @param list (list) List of ggplot2 objects.
#' @param filename (chr) What to call the pdf.
#'
#' @return Invisible NULL.
#' @export
#'
#' @examples
#' #plot histogram of each numeric variable in iris
#' list_iris = map(names(iris[-5]), ~ggplot(iris, aes_string(.)) + geom_histogram())
#' #save to a single pdf
#' GG_save_pdf(list_iris, "test.pdf")
GG_save_pdf = function(list, filename) {
  #start pdf
  pdf(filename)

  #loop
  for (p in list) {
    print(p)
  }

  #end pdf
  dev.off()

  invisible(NULL)
}

Answer 5

A nice solution without the gridExtra package:

library(plyr)
library(ggplot2)

li = structure(p, class = c("gglist", "ggplot"))
print.gglist = function(x, ...) l_ply(x, print, ...)
ggsave(li, file = "test.pdf")

Answer 6

This solution is independent of whether the lengths of the lists in the list p are different.

library(gridExtra)

pdf("plots.pdf", onefile = TRUE)
for (i in seq(length(p))) {
  do.call("grid.arrange", p[[i]])  
}
dev.off()

Because of onefile = TRUE the function pdf saves all graphics appearing sequentially in the same file (one page for one graphic).