fixed "number" of plots using facet_wrap

Question

If I have a data.frame dat and want to plot groups of data using facet_wrap:

dat <- data.frame(x = runif(150), y = runif(150), z = letters[1:15])

ggplot(dat[dat$z %in% letters[1:9], ], aes(x, y)) +
  geom_point() +
  facet_wrap( ~ z, ncol = 3, nrow = 3)

This looks great and performs as expected. However, if I plot the next set of z on a new plot:

ggplot(dat[dat$z %in% letters[10:15], ], aes(x, y)) +
  geom_point() +
  facet_wrap( ~ z, ncol = 3, nrow = 3)

I no longer have 3 rows and 3 columns. I can fix the aspect ratios of the plots using opts(aspect.ratio = 1) but I still have them laid out differently that my previous plot. I'd like it to appear as though there are always 9 plots on the page even if there are 6 or 1. Is that possible?

Answer 1

Try this,

library(ggplot2)
library(plyr)
library(gridExtra)

dat <- data.frame(x=runif(150), y=runif(150), z=letters[1:15])

plotone = function(d) ggplot(d, aes(x, y)) + 
  geom_point() + 
  ggtitle(unique(d$z))

p = plyr::dlply(dat, "z", plotone)
g = gridExtra::marrangeGrob(grobs = p, nrow=3, ncol=3)
ggsave("multipage.pdf", g)

Answer 2

library(cowplot) provides a handy function plot_grid that we can use to arrange a list of plots.

First, lets construct the list of individual plots:

p = lapply(unique(dat$z), function(i){
      ggplot(dat[dat$z == i, ], aes(x, y)) +
        geom_point() +
        facet_wrap(~z)
        })

Now we can arrange the panels using plot_grid:

plot_grid(plotlist = p[1:9], nrow = 3, ncol = 3)

plot_grid(plotlist = p[10:15], nrow = 3, ncol = 3)

Answer 3

For anyone coming to this late like me, you can use facet_wrap_paginate from ggforce to keep using ggplot2. Help file says: "This extension to ggplot2::facet_wrap() will allow you to split a facetted plot over multiple pages." Something like the following will work:

library(ggplot2)
library(ggforce)
data("diamonds")
ggplot(diamonds) +
  geom_point(aes(carat, price), alpha = 0.1) +
  facet_wrap_paginate(~clarity, ncol = 2, nrow = 2, page = 2)

Use page to select which page you want to view or wrap in a loop to display all in a document.