Map over some numeric columns and for each boxplot with a grouping var

Question

I would like to purrr::map over a df and for each column produce a boxplot with a grouping var. Example attempt:

mtcars |> select(am, gear, carb) |> 
  map(~ ggplot() +
        geom_boxplot(aes(y = .x, fill = factor(mtcars$cyl))) +
        labs(title = .y))

Outcome:

Error in dots_list(..., title = title, subtitle = subtitle, caption = caption, : the ... list contains fewer than 2 elements

Desired outcome:

1. .x would be the vector/field from the df
2. Using the native pipe placeholder _, assign the grouping var cyl
3. The title would be the name of the column being plotted. I'm sure I recall seeing .y being used here before

How can I purrr::map over the 3 columns am, gear and carb, for each produce a boxplot grouped/split by cyl and using hte native pipe?

Answer 1

With purrr::map, it will not define .y, but I'm inferring that you intend for it to be the column name. Use purrr::imap and your code works.

library(dplyr)
library(purrr)
library(ggplot2)
mtcars |> select(am, gear, carb) |> 
  imap(~ ggplot() +
        geom_boxplot(aes(y = .x, fill = factor(mtcars$cyl))) +
        labs(title = .y))

Optional, I made the above triple plot with patchwork:

library(patchwork)
map(c("am", "gear", "carb"), ~ mtcars |> 
      ggplot() +
        geom_boxplot(aes(y = .data[[.x]], fill = as.factor(cyl))) +
      labs(title = .x)) |>
  Reduce(`+`, x = _)

... though this also be done more easily with faceting.