ggplot2: multiple plots with different variables in a single row, single grouping legend

Question

While there are some topics going in the same general direction, I haven't found any that would deal with my issue specifically. Hence a new topic, and thanks in advance for all the help.

Situation

I have two plots, that need to go in a single figure horizontally, e.g.:

library(ggplot2)
dsamp <- diamonds[sample(nrow(diamonds), 1000), ]    
p1 <- qplot(price, carat, data=dsamp, colour=clarity)
p2 <- qplot(price, depth, data=dsamp, colour=clarity)

While the dependent variable differs per plot, the grouping and the independent remains the same. Hence I only need but a single legend in the figure to describe the groups.

What I have tried and what did not work

I have tried to use the solution as described in the R Cookbook. The custom multiplot() function given on that page renders the plots without legends just fine. However, if one needs only a single legend, that function fails. Since one of the graphs would contain the legend, whereas the other not, the width of both graphs would differ in relation to each other (copy the multiplot function from the link mentioned please):

multiplot(p1 + theme(legend.position = "none"),p2,cols=2)

Another potential solution that I have found is the package gridExtra, with this code example. It almost does what I need, except that the graphs are arranged vertically. I tried playing with the function arguments, but could not figure how to arrange the plots horizontally. Hope someone has more experience with that package/issue. Thanks!

Who stumbles upon this question: I have asked a very similar one and you might find the answers there very useful. stackoverflow.com/questions/34814478/… — mts
– mts, Commented Jan 16, 2016 at 0:04

Community · Accepted Answer · 2017-05-23 12:16:56Z

16

Here is solution using package gridExtra and grid.arrange(). First, make three plots - one with legend (p1.leg) and two without legends.

p1.leg <- ggplot(dsamp,aes(price,carat,colour=clarity))+geom_point()
p1<-ggplot(dsamp,aes(price,carat,colour=clarity))+geom_point()+
      theme(legend.position="none")
p2 <-ggplot(dsamp,aes(price,depth,colour=clarity))+geom_point()+
     theme(legend.position="none")

Now you can get just legend from the first plot with function g_legend() that I borrowed from @Luciano Selzer answer to this question.

g_legend <- function(a.gplot){
  tmp <- ggplot_gtable(ggplot_build(a.gplot))
  leg <- which(sapply(tmp$grobs, function(x) x$name) == "guide-box")
  legend <- tmp$grobs[[leg]]
  return(legend)}

leg<-g_legend(p1.leg)

Now you can combine both plots and legend with functions arrangeGrob() and grid.arrange(). In arrangeGrob() you can set widths for columns to get desired proportion between plots and legend.

library(gridExtra)
grid.arrange(arrangeGrob(arrangeGrob(p1,p2),leg,ncol=2,widths=c(5/6,1/6)))

enter image description here

UPDATE

To put all plots in the same row:

grid.arrange(arrangeGrob(p1,p2,leg,ncol=3,widths=c(3/7,3/7,1/7)))

enter image description here

edited May 23, 2017 at 12:16

CommunityBot

11 silver badge

answered Jun 6, 2013 at 13:30

Didzis Elferts

99.2k17 gold badges275 silver badges207 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Maxim.K Over a year ago

Thank you, Didzis. Unfortunately, this is not what I need. It is the solution which is mentioned in the example for the gridExtra package (at least it has the same result). What I need is to have these graphs and legend arranged horizontally, not vertically. Could you possibly modify the grid.arrange() call to achieve that? Thank you.

smillig Over a year ago

Just add ncol=2 to the arrangeGrob(p1, p2) part of the code. (e.g. arrangeGrob(p1, p2, ncol=2)).

Didzis Elferts Over a year ago

Updated my answer to put all plots in one row.

baptiste Over a year ago

you don't have to manually guess the legend width: github.com/hadley/ggplot2/wiki/…

Collectives™ on Stack Overflow

ggplot2: multiple plots with different variables in a single row, single grouping legend

1 Answer 1

UPDATE

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

UPDATE

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related