I have a simple geom_point plot, in which the x variable is ordinal, taking 5 values (coded 1:5).
In the plot I would like to replace it with 5 corresponding text labels. Is it possible to do it in ggplot?
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4 Answers
You should be able to do this with scale_x_discrete.
library(ggplot2) df <- data.frame(x = 1:5, y = sample(1:10, 5, TRUE)) qplot(factor(x),y, data = df) + scale_x_discrete(breaks = 1:5, labels=c("foo","bar","baz","phi","fum")) + xlab(NULL) 
4 Comments
Chase
@gappy - the key here is to convert your x-axis to a factor. The solution that @prasad and I provided does this in the ggplot call itself (the
factor(x) and ordered(x) bit), while @Gavin's handles it in a preprocessing step. The end result of all three answers is that the x-axis is treated as a factor before plotting.
Gavin Simpson
@gappy your data are what R would consider a factor - at least from the brief description you give. Can the data take a value of 1.5 say? If they can what label should those data points get? If your data are ordinal, then you should tell R this and store as / coerce to a factor (
factor()) or ordered factor (ordered()). If you do, it will do the right thing in many cases. See my answer - the correct plot is drawn if you tell R that the data are a factor. The answers of @Chase and @Prasad coerce as part of the plot and allow of run-time customisation of the labels.Chase
@Gavin - run-time customization of labels...very nice way to summarize what the three of us danced around in the last 6 comments.
Al14
not always scale_x_discrete works, instead scale_x_continuous should utilised
scale_x_discrete should do it:
x <- sample(1:5, 20, T) y <- rnorm(20) + x df <- data.frame(x = ordered(x), y = y) ggplot(df,aes(x,y)) + geom_point() + scale_x_discrete(breaks = 1:5, labels = letters[1:5]) 
4 Comments
Gavin Simpson
not being a big ggplot user, isn't
scale_x_discrete implied if x is a factor? If so, is there an advantage to calling it directly rather then getting the factor labels correct in the data? I could ask the same of @Chase as (s)he has supplied the same answer?
Prasad Chalasani
@Gavin you're right --
scale_x_discrete is only used to override the default factor labels. I guess it's useful if you have one data-frame, and you want to plot it differently in different situations (i.e. use different labels each time), so that way you don't have to change the data-frame each time.Chase
@Gavin & @Prasad - I understood the OPs question to mean that he had numeric values that he wanted to represent as categorical, or ordinal in this case. Interesting that Prasad & I essentailly developed the same answer. Is there a preference for
ordered() over factor()?Gavin Simpson
@Chase I get that - all three of our answers do the same thing (AFAICT) just from two different viewpoints. My preference would be to alter the data to be stored correctly hence my answer; was just wondering about the pros/cons of
scale_x_discrete().Here is a reproducible example I think encapsulates your Q (?):
require(ggplot2) dat <- data.frame(X = sample(1:5, 100, replace = TRUE), Y = rnorm(100)) It isn't immediately clear what data you have, but if you mean something like this:
(p1 <- ggplot(dat, aes(x = X, y = Y)) + geom_point()) Then I think you want a stripchart, which can be achieved in ggplot via a factor
dat2 <- within(dat, X <- factor(X, labels = letters[1:5])) (p2 <- ggplot(dat2, aes(x = X, y = Y)) + geom_point()) If this isn't what you mean, can you edit your Q to provide an example?
Comments
Another option using scale_x_continuous where the breaks and labels are specified on a numerical continuous axis. Here is some reproducible code:
library(ggplot2) df <- data.frame(x = 1:5, y = sample(1:10, 5, TRUE)) ggplot(df, aes(x = x, y = y)) + geom_point() + scale_x_continuous(breaks = c(1:5), labels = c("A", "B", "C", "D", "E")) 
Created on 2023-02-03 with reprex v2.0.2
