Saving multiple ggplots at the same time

Question

I am running a lot of graphs across different subsets of data, using the split function with the lapply function.

My problem is: How do I easily save all the graphs? Ideally I want to name each fileby the title of the graph (Indicating the subset of data).

data("mtcars")

split <- split(mtcars, list(mtcars$gear, mtcars$am))

my_plot <- function(mtcars) {
  ggplot(mtcars, aes(x=mpg, y=cyl)) + 
  geom_point() +
  labs (title= paste(unique(mtcars$gear), paste("- ", unique(mtcars$am)))) }

lapply(split, my_plot)

Thus far, I have been saving the temporary directory (But this is a lot of manual labour)

plots.dir.path <- list.files(tempdir(), pattern="rs-graphics", full.names = TRUE); 
plots.png.paths <- list.files(plots.dir.path, pattern=".png", full.names = TRUE)
file.copy(from=plots.png.paths, to="......")

Answer 1

You could include ggsave in your function, then we would loop over the names() of split instead:

data("mtcars")
library(ggplot2)

split <- split(mtcars, list(mtcars$gear, mtcars$am))

my_plot <- function(x) {
  p <- ggplot(split[[x]], aes(x=mpg, y=cyl)) + 
    geom_point() +
    labs (title= paste(unique(split[[x]][["gear"]]), paste("- ", unique(split[[x]][["am"]]))))
  
  ggsave(paste0("my_path/mtcars_", x, ".png"))
  p  
}

lapply(names(split), my_plot)

Alternatively we could use a slightly different workflow with purrr::map and purrr::iwalk(). First we create a list of plots with purrr::map and than loop over the named lists of plots using purrr::iwalk() to save them:

library(purrr)

my_plot <- function(df, nm) {
  ggplot(df, aes(x=mpg, y=cyl)) + 
    geom_point() +
    labs (title= paste(unique(df[["gear"]]), paste("- ", unique(df[["am"]]))))
}

# save plots to list
plots <- map(split, my_plot)

# loop over plots and save
iwalk(plots, ~ ggsave(paste0("my_path/mtcars_", .y, ".png"),
                     plot = .x))

^{Created on 2023-02-16 by the reprex package (v2.0.1)}