ggplot how to edit axis labels in R

Question

I have a dataframe to plot where y_axis variable is a character one. I want to take only the last part of character with '_' as separation.

Here an example with iris dataset. As you can see, all y_axis labels are the same. How can I do it? thanks

iris$trial = paste('hello', 'good_bye', iris$Sepal.Length, sep = '_')

myfun = function(x) {
  tail(unlist(strsplit(x, '_')), n = 1)
}

ggplot(iris, aes(x = Species, y = trial, color = Species)) +
  geom_point() +
  scale_y_discrete(labels = function(x) myfun(x)) +
  theme_bw()

Why not use Sepal.length as a y-axis but first paste it and then strsplit it? stackoverflow.com/questions/41336606/… provides an answer on how to access elements of strsplit — maarvd
– maarvd, Commented May 10, 2021 at 11:12
I've used Sepal.Length because my problem variable, has characters + numeric. And I only want the numeric one. I cannot edit this variable on dataframe, because color variable needs all character+numeric, because color value is a named vector with character+numeric and I shouldn't edit those names, because it would contain duplicates — Archymedes
– Archymedes, Commented May 10, 2021 at 11:18

Annet · Accepted Answer · 2021-05-10 11:15:21Z

1

It seems to me that you function is only applied to the first row of the column. That value is replicated. Using lapply returns all the unique values. However, I don't know if it makes sense in this example without making it numeric (and sorting it) so you might want to add that as well.

ggplot(iris, aes(x = Species, y = trial, color = Species)) +
  geom_point() +
  scale_y_discrete(labels = lapply(iris$trial, myfun)) +
  theme_bw()

answered May 10, 2021 at 11:15

Annet

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1 Comment

Archymedes Over a year ago

Awesome!! lapply solved the problem. I thought it would be applied automatically, but recursive is needed here. Thanks

Ronak Shah · Accepted Answer · 2021-05-10 12:16:04Z

0

You can make use of regex instead to extract the required value.

library(ggplot2)

#This removes everything until the last underscore
myfun = function(x) sub('.*_', '', x)

ggplot(iris, aes(x = Species, y = trial, color = Species)) +
  geom_point() +
  scale_y_discrete(labels = myfun) +
  theme_bw()

If you want to extract numbers from y-axis value, you can also use scale_y_discrete(labels = readr::parse_number).

answered May 10, 2021 at 12:16

Ronak Shah

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