drawing multiple plots, 2 per page using ggplot

Question

I have a list of dataframes and I would like to print them all in a .RMarkdown document with 2 per page. However, I have not been able to find a source for doing this. Is it possible to do this via a for loop?

What I would like to achieve is something with the following idea:


listOfDataframes <- list(df1, df2, df3, ..., dfn)

for(i in 1:){
   plot <- ggplot(listOfDataframes[i], aes(x = aData, y = bData)) + geom_point(color = "steelblue", shape = 19)

 #if two plots have been ploted break to a new page.

}

Is this possible to achieve with ggplot in rmarkdown? I need to print out a PDF document.

Just to clarify, will your output PDF only have plots in it or do you have additional info in a Markdown document? I've seen a fair number of related questions to help with outputting plots to a PDF (`gridExtra::marrangeGrob()` might be worth exploring) but not as much in Rmd. — aosmith, Jul 09 '21 at 15:45
Well, I have seen some examples too, but I have not seen the actual code for example to output 2 plots per page. How will it be the code If I want to output 2 plots per page only in the Rmarkdown but I want to change the plot titles on each plot.?? thanks — JK Lambert, Jul 09 '21 at 16:09
So you want plots within a larger R markdown that outputs PDF not a sep PDF of plots? Some ideas: 1. Combine the plots into pairs with, e.g., **patchwork** or **cowplot** and then insert page breaks along [these lines](https://stackoverflow.com/questions/31830974/inserting-a-page-break-within-a-code-chunk-in-rmarkdown-converting-to-pdf)? (Maye there is a newer option for page breaks?) 2. Stack all datasets together with an ID column and loop through with `ggforce::facet_wrap_paginate()` a la [this](https://stackoverflow.com/a/48544261/2461552) but within Rmd not `pdf()`. — aosmith, Jul 09 '21 at 16:28

AndrewGB · Accepted Answer · 2021-09-17T16:01:33.583

If you just need to output plots with two per page, then I would use gridExtra as was suggested above. You could do something like this if you were to put your ggplot objects into a list.

library(ggplot2)
library(shinipsum) # Just used to create random ggplot objects.
library(purrr)
library(gridExtra)

# Create some random ggplot objects.
ggplot_objects <- list(random_ggplot("line"), random_ggplot("line"))

# Create a list of names for the plots.
ggplot_objects_names <- c("This is Graph 1", "This is Graph 2")

# Use map2 to pass the ggplot objects and the list of names to the the plot titles, so that you can change them.
ggplot_objects_new <-
  purrr::map2(
    .x = ggplot_objects,
    .y = ggplot_objects_names,
    .f = function(x, y) {
      x + ggtitle(y)
    }
  )

# Arrange each ggplot object to be 2 per page. Use marrangeGrob so that you can save two ggplot objects per page.
ggplot_arranged <-
  gridExtra::marrangeGrob(ggplot_objects_new, nrow = 2, ncol = 1)

# Save as one pdf. Use scale here in order for the multi-plots to fit on each page.
ggsave("ggplot_arranged.pdf",
       ggplot_arranged, scale = 1.5)

If you have a list of dataframes that you are wanting to create ggplots for, then you can use purrr::map to do that. You could do something like this:

purrr::map(df_list, function(x) {
  ggplot(data = x, aes(x = aData, y = bData)) +
    geom_point(color = "steelblue", shape = 19)
})

drawing multiple plots, 2 per page using ggplot

1 Answers1