How to align plots (ggplot2) horizontally?

Question

Hello R and ggplot2 community!

I would like to horizontally align two plots, produced with ggplot2. One has both facets (and facet strips!) and legend, but the second hasn't. They share the same Y axis, which I would like to align. I'm ok to vertically align plots using their grobs' widths, but I couldn't figure it out with heights.

Here is a piece of code to support my question.

library( ggplot2 )
library( gridExtra )

plot_1 <- ggplot() +
  geom_point(
    data = iris,
    aes(
      x = Petal.Length,
      y = Petal.Width,
      colour = Sepal.Length 
      ) 
    ) +
  facet_grid(
    . ~ Species 
    ) +
  theme(
    legend.position = "bottom"
    )

plot_2 <- ggplot() +
  geom_point(
    data = iris,
    aes(
      x = Sepal.Width,
      y = Petal.Width
      )
    )

g1 <- ggplotGrob( plot_1 )
g2 <- ggplotGrob( plot_2 )

# Here, how to manipulate grobs to get plot_2 scaled to the plot_1's Y axis? (ie, with an empty area right of the plot_1's legend)

grid.arrange( g1, g2, ncol = 2 )

Do you know how to manipulate grobs' heights before grid.arrange()? (Any other suggestion is welcome!) Additionally, how to assign, say, two thirds of the total area to plot_1?

Note also that my real plots actually feature a coord_flip(), but I assumed it's not relevant for this question.

Thanks for your help!

Pewi Pewi · Accepted Answer · 2015-03-23T14:58:31

A simple solution is to create a blank panel:

blank<-grid.rect(gp=gpar(col="white"))

Then use grid.arrange in order to create a two column grid in which the second column actually consists of three rows.

grid.arrange(g1, arrangeGrob(blank,g2,blank,ncol=1,
heights=c(0.2,0.9,0.2)),ncol=2)

Playing around with the heights argument should provide us with the desired result.

Regarding your additional question the heights and widthsarguments of grid.arrangeshould prove quite useful there aswell.

How to align plots (ggplot2) horizontally?

1 Answers