ggplot: modify axis labels with named vector after having applied function

Question

I have a question regarding the modification of axis labels in ggplot. I know that what I am trying to get at can be done via other means (e.g. creating a new column with case_when). My interest is in the approach/concept outlined below.

Let's say I have a discrete variable at the x-axis. In order to get the desired axis labels, the values are 1) modified with a function, and then 2) changed by assigning the values contained in a named vector to the result of the function. I am able to do each of the two steps individually; but how can they be combined? Can this be done?

Again, I am aware that there are other, probably more sane ways, to do this. And the example below doesn't make any substantive sense. I am just curious whether/how this can be done directly in the e.g. scales_x_discrete function. Below I am trying to detail what I mean. The result would be that all Merc labels become Mercedes, and all instances of Hornet become Super Hornet.

library(tidyverse)

labeller_cars <- c("Hornet"="Super Hornet",
                   "Merc"="Mercedes")

mtcars %>% 
  rownames_to_column(var = "name") %>% 
  filter(str_detect(name, regex("Hornet|Merc"))) %>% 
  ggplot()+
  geom_bar(aes(x=name,
               y=disp),
           stat="identity")+
  #here is what I am interested in; this works, but it's only first step
  scale_x_discrete(labels=function(x) str_extract(x, regex("[:alpha:]*")))
  #this is an attempt, but doesn't work.
  # scale_x_discrete(labels=function(x) str_extract(x, regex("[:alpha:]*")) %>% labeller_cars)

^{Created on 2021-07-24 by the reprex package (v2.0.0)}

akrun · Accepted Answer · 2021-07-24 22:46:33Z

2

We could use str_replace_all instead of str_extract

library(dplyr)
library(stringr)
library(ggplot2)
labeller_cars <- c(".*Hornet.*"="Super Hornet",
                    ".*Merc.*"="Mercedes")
mtcars %>% 
   rownames_to_column(var = "name") %>% 
   filter(str_detect(name, regex("Hornet|Merc"))) %>% 
   ggplot()+
   geom_bar(aes(x=name,
                y=disp),
            stat="identity")+
   #here is what I am interested in; this works, but it's only first step
   scale_x_discrete(labels=function(x) str_replace_all(x, labeller_cars)) + 
 theme(axis.text.x = element_text(angle = 90, vjust = 0.5, hjust=1))

-output

Or with str_extract, after extracting the substring, use the named vector to match and replace

labeller_cars <- c("Hornet"="Super Hornet",
                    "Merc"="Mercedes")
mtcars %>% 
   rownames_to_column(var = "name") %>% 
   filter(str_detect(name, regex("Hornet|Merc"))) %>% 
   ggplot()+
   geom_bar(aes(x=name,
                y=disp),
            stat="identity")+
   scale_x_discrete(labels=function(x)
      labeller_cars[str_extract(x, regex("[:alpha:]*"))])

-OUTPUT

edited Jul 24, 2021 at 22:46

answered Jul 24, 2021 at 22:11

akrun

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3 Comments

zoowalk Over a year ago

many thanks. I realize my example is not very good since with the intended results 2 columns would be called "Super Hornet" and all others would be called "Mercedes". What I am interested is to modify labels via a named vector AFTER having applied a function to the labels (here - str_extract, which lumps all Hornets and Merc together). –

zoowalk Over a year ago

many thanks for your reply and apologies if I am not clear enough. str_extract ìn my example results in multiple Hornet and Merc (since it takes only this part from the labels). This was the first step. Now I would like to match (?) these results with a named vector to get the final label. The function str_extract is only used here as an example. The point i am interested in is how can I use the outcome of a function (used in scale_x_discrete(labels=...) to match it w named vector. I work with examples where I use str_remove etc. I assume I somehow ve to integrate this into my fn.

zoowalk Over a year ago

the second solution is what I was looking for. thanks again.

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