Plot axes with customized labels

November 11, 2013

(This article was first published on Milano R net, and kindly contributed to R-bloggers)

How to modify axis labels is a FAQ for (almost) all R users.

This short post try to give a simple but exhaustive reply to this question.

First of all, data are generated.

?View Code RSPLUS
dat = data.frame(
  label = sample(c(1, 2, 3), 150, replace = TRUE),
  val = rgamma(150, 50)

A boxplot of the numeric variable val can be generated for each group.

?View Code RSPLUS
boxplot(dat$val ~ dat$label)

The simplest way to add a label for groups is treating the label variable as a factor. This is the best choice also from a logical point of view.

?View Code RSPLUS
dat$label = factor(
  dat$label, levels = 1:3,
  labels = c("First", "Second", "Third")

Wow! Now the plot show the group names.

?View Code RSPLUS
boxplot(dat$val ~ dat$label)

If labels change, factor can be modified in a one line.

?View Code RSPLUS
levels(dat$label) = c(
  "My First Group has a very long name",
  "My Second Group is a little bit more long",
  "The third one is as long as the first"

And again, my plot!

?View Code RSPLUS
boxplot(dat$val ~ dat$label)

The labels are too long and the second one doesn't appear. Labels may be rotated, using the las parameter. This argument specifies the style of axis labels. It can assume one of the following: 0 (always parallel to the axis, which is the default), 1 (always horizontal), 2 (always perpendicular to the axis), 3 (always vertical).

?View Code RSPLUS
boxplot(dat$val ~ dat$label, las = 3)

Labels have been rotated, but labels go outside the margin and disappears. Bottom margin should be increased. This can be done using the mar argument of the par() function. The default is par(mar = c(5,4,4,2)) which means that there are 5 lines at the bottom, 4 lines on the left, 4 lines in the top and 2 lines on the right. The bottom margin can be increased to 20 lines.

?View Code RSPLUS
op0 = par()    # Get current graphical parameters
op1 = op0$mar  # Get current margins in lines
op1[1] = 20    # Modify bottom margins to 20 (lines)
op1            # View bottom margins in lines
?View Code OUTPUT
## [1] 20.0  4.1  4.1  2.1

If you want to specify margins in inches, use par(mai = c(bottom, left, top, right).

Now I obtained the plot I was looking for!

?View Code RSPLUS
par(mar = op1)
boxplot(dat$val ~ dat$label, las = 3)

Next article will show how to manage axis, add/remove ticks and modify labels out of data structure, i.e. without modify factors.

To leave a comment for the author, please follow the link and comment on their blog: Milano R net. offers daily e-mail updates about R news and tutorials on topics such as: Data science, Big Data, R jobs, visualization (ggplot2, Boxplots, maps, animation), programming (RStudio, Sweave, LaTeX, SQL, Eclipse, git, hadoop, Web Scraping) statistics (regression, PCA, time series, trading) and more...

If you got this far, why not subscribe for updates from the site? Choose your flavor: e-mail, twitter, RSS, or facebook...

Comments are closed.


Mango solutions

RStudio homepage

Zero Inflated Models and Generalized Linear Mixed Models with R

Quantide: statistical consulting and training


CRC R books series

Contact us if you wish to help support R-bloggers, and place your banner here.

Never miss an update!
Subscribe to R-bloggers to receive
e-mails with the latest R posts.
(You will not see this message again.)

Click here to close (This popup will not appear again)