Writing to the global environment from a function in R - r

Question

Im new to R and have some trouble understanding how to handle local and global environments. I checked the Post on local and global variables, but couldn't figure it out.
If, for example, I would like to make several plots using a function and save them like this:
PlottingFunction <- function(type) {
type <<- mydata %>%
filter(typeVariable==type) %>%
qplot(a,b)
}
lapply(ListOfTypes, PlottingFunction)
Which didn't yield the desired result. I tried using the assign() function, but couldn't get it to work either.
I want to save the graphs in the global environment so I can combine them using gridExtra. This might not be the best way to do that, but I think it might be useful to understand this issue nevertheless.

Answer 1

You don't need to assign the plot to a gloabl variable. All plots can be saved in one list.
For this example, I use the iris data set.
library(gridExtra)
library(ggplot2)
library(dplyr)
str(iris)
# 'data.frame': 150 obs. of 5 variables:
# $ Sepal.Length: num 5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...
# $ Sepal.Width : num 3.5 3 3.2 3.1 3.6 3.9 3.4 3.4 2.9 3.1 ...
# $ Petal.Length: num 1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 ...
# $ Petal.Width : num 0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.2 0.2 0.1 ...
# $ Species : Factor w/ 3 levels "setosa","versicolor",..: 1 1 1 1 1 1 1 1 1 1 ...
The modified function without assignment:
PlottingFunction <- function(type) {
iris %>%
filter(Species == type) %>%
qplot(Sepal.Length, Sepal.Width, data = .)
}
One figure per Species is created
species <- unique(iris$Species)
# [1] setosa versicolor virginica
# Levels: setosa versicolor virginica
l <- lapply(species, PlottingFunction)
Now, the function do.call can be used to call grid.arrange with the plot objects in the list l.
do.call(grid.arrange, l)