r - Align plot areas in ggplot

Question

I am trying to use grid.arrange to display multiple graphs on the same page generated by ggplot. The plots use the same x data but with different y variables. The plots come out with differing dimensions due to the y-data having different scales.

I have tried using various theme options within ggplot2 to change the plot size and move the y axis label but none have worked to align the plots. I want the plots arranged in a 2 x 2 square so that each plot is the same size and the x-axes align.

Here is some test data:

A <- c(1,5,6,7,9)
B <- c(10,56,64,86,98)
C <- c(2001,3333,5678,4345,5345)
D <- c(13446,20336,24333,34345,42345)
L <- c(20,34,45,55,67)
M <- data.frame(L, A, B, C, D)

And the code that I am using to plot:

x1 <- ggplot(M, aes(L, A,xmin=10,ymin=0)) + geom_point() + stat_smooth(method='lm')
x2 <- ggplot(M, aes(L, B,xmin=10,ymin=0)) + geom_point() + stat_smooth(method='lm')
x3 <- ggplot(M, aes(L, C,xmin=10,ymin=0)) + geom_point() + stat_smooth(method='lm')
x4 <- ggplot(M, aes(L, D,xmin=10,ymin=0)) + geom_point() + stat_smooth(method='lm')
grid.arrange(x1,x2,x3,x4,nrow=2)

If you run this code, you will see that the bottom two plots have a smaller plot area due to the greater length of the y-axes units.

How do I make the actual plot windows the same?

Answer 1

Edit

Simpler solutions are: 1) use the cowplot package (see answer here); or 2) use egg package available on github.

# devtools::install_github("baptiste/egg")
library(egg)
library(grid)

g = ggarrange(x1, x2, x3, x4, ncol = 2)
grid.newpage()
grid.draw(g)

Original

Minor edit: Updating code.

If you want to keep the axis labels, then with some fiddling, and borrowing code from here, this does the job.

library(ggplot2)
library(gtable)
library(grid)
library(gridExtra)

# Get the widths
gA <- ggplotGrob(x1)
gB <- ggplotGrob(x2)
gC <- ggplotGrob(x3)
gD <- ggplotGrob(x4)
maxWidth = unit.pmax(gA$widths[2:3], gB$widths[2:3], 
                     gC$widths[2:3], gD$widths[2:3])

# Set the widths
gA$widths[2:3] <- maxWidth
gB$widths[2:3] <- maxWidth
gC$widths[2:3] <- maxWidth
gD$widths[2:3] <- maxWidth

# Arrange the four charts
grid.arrange(gA, gB, gC, gD, nrow=2)

ALTERNATIVE SOLUTIONS: There are rbind and cbind functions in the gtable package for combining grobs into one grob. For the charts here, the widths should be set using size = "max", but the CRAN version of gtable throws an error.

One option is to examine the grid.arrange plot, then use size = "first" or size = "last"` options:

# Get the ggplot grobs
gA <- ggplotGrob(x1)  
gB <- ggplotGrob(x2)
gC <- ggplotGrob(x3)
gD <- ggplotGrob(x4)

# Arrange the four charts
grid.arrange(gA, gB, gC, gD, nrow=2)

# Combine the plots   
g = cbind(rbind(gA, gC, size = "last"), rbind(gB, gD, size = "last"), size = "first")

# draw it
grid.newpage()
grid.draw(g)

A second option is to binding functions from gridExtra package.

# Get the ggplot grobs
gA <- ggplotGrob(x1)  
gB <- ggplotGrob(x2)
gC <- ggplotGrob(x3)
gD <- ggplotGrob(x4)

# Combine the plots
g = cbind.gtable(rbind.gtable(gA, gC, size = "max"), rbind.gtable(gB, gD, size = "max"), size = "max")

# Draw it
grid.newpage()
grid.draw(g)