ggplot2: how to assign value of variable to ggplot title

Question

How can I assign the value of a variable to a ggplot title after filtering the underlying dataframe 'in one go'.

library(tidyverse)

#THIS WORKS
d <- mtcars %>% 
  filter(carb==4)

d %>% 
  ggplot()+
  labs(title=paste(unique(d$carb)))+
  geom_bar(aes(x=am,
               fill=gear),
           stat="count")



#THIS DOESN'T WORK

mtcars %>% 
  filter(carb==4) %>% 
  ggplot()+
  labs(title=paste(data=. %>% distinct(carb) %>% pull()))+
  geom_bar(aes(x=am,
               fill=gear),
           stat="count")
#> Error in as.vector(x, "character"): cannot coerce type 'closure' to vector of type 'character'

#THIS ALSO DOESN'T WORK

mtcars %>% 
  filter(carb==3) %>% 
  ggplot()+
  labs(title=paste(.$carb))+
  geom_bar(aes(x=am,
               fill=gear),
           stat="count")
#> Error in paste(.$carb): object '.' not found

^{Created on 2020-04-23 by the reprex package (v0.3.0)}

akrun · Accepted Answer · 2020-04-23 20:40:02Z

6

We can wrap the code block with {} and use .$

library(dplyr)
library(ggplot2)
mtcars %>% 
  filter(carb==4) %>% {
  ggplot(., aes(x = am, fill = gear)) +
       geom_bar(stat = 'count') +
       labs(title = unique(.$carb))
   }

-output

answered Apr 23, 2020 at 20:40

akrun

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2 Comments

MorrisseyJ Over a year ago

this works perfectly. Any chance you could explain what it does. Searching seems to only bring up r.markdown explanations.

akrun Over a year ago

@MorrisseyJ It is more easier to understand if you assign the output at the filter step to a new object i.e. d1 <- mtcars %>% filter(carb==4) then it is just ggplot(d1, aes(x = am, fill = gear)) + geom_bar(stat = 'count') + labs(title = unique(d1$carb)). Wrapping within a {} allows to consider it as a single block and we can extract the values of columns from the previous step i..e the 'carb' column

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