using a custom ggplot function in a loop of variables from a list

Question

I want to use a very simple custom ggplot2 call inside a loop. Taking a list of variables from a dataframe to feed my function I want to obtain a plot for every variable.

This is a simplified example just for ilustrating my issue. The real function is more complex.

Function alone worked ok, but inside a loop is not working.

library(rlang) 
library(ggplot2)

gg_hist <- function(data, x){
  ggplot(data,
         aes(x = {{ x }} )) + 
    geom_histogram()
}

# This works ok

gg_hist(mtcars, hp)


# my list of variables to loop

vars <- c("mpg","hp")

for (variable in vars) {
  p <- gg_hist(mtcars, {{ variable }})
  print(p)
}


# unquoting list of variables not working either

vars <- c(mpg,hp)

You can use quos. Either vars <- quos(mpg, hp) and then your for loop. Or something like lapply(quos(mpg, hp), gg_hist, data = mtcars). Alternatively, use aes_ or aes_string instead of aes, all depending on preference. — Axeman
– Axeman, Commented Nov 5, 2020 at 17:58

luismf · Accepted Answer · 2020-11-06 19:44:33Z

2

Unless for some reason you want to be able to pass unquoted parameters, I would change the function so it only admits strings and use the .data[[]] pronoun which is the recommended way in the last versions of dplyr and ggplot. Its purpose is obvious to read when compared with quotes and bangs !! (Although someone may argue the opposite).

library(ggplot2)

gg_hist <- function(data, x){
  ggplot(data,
         aes(x = .data[[x]] )) + 
    geom_histogram()
}

gg_hist(mtcars, "hp") # Note now I use "hp" and not hp

vars <- c("mpg","hp")

for (variable in vars) {
  p <- gg_hist(mtcars, variable)
  print(p)
}

The main source for this would be the dplyr official documentation. It is true that is not a gpplot2 source but most of what is explained there is applicable. Other source for ggplot2 especifically is this rconf2020 slides. Hope this helps.

edited Nov 6, 2020 at 19:44

answered Nov 5, 2020 at 19:28

luismf

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2 Comments

Forge Over a year ago

This worked ok but I would be very grateful for adding documentation links on this obscure concept

luismf Over a year ago

I have added some sources in the answer. Hope it clarifies it a bit!

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