In this tutorial, we will learn how to make a plot using ggplot2 such that the column name of interest in a plot is saved as a variable. And we are interested in using the variable name to make a boxplot. The ability to use a column name as a variable help us make more generalizable plot, for example writing a function to make a plot.
Let us get started by loading the packages. dplyr/ggplot2’s tidy evaluation methods enable us to use a variable while plotting. Therefore, let us also verify the ggplot2/dplyr versions.
1 2 3 4 5 6 7 | library(tidyverse)library(palmerpenguins)theme_set(theme_bw(16))packageVersion("dplyr")[1] '1.1.2'packageVersion("ggplot2")[1] '3.4.3' |
In the Palmer penguins data, we will be making a boxplot between species column and flipper_length_mm column.
1 2 3 4 5 6 7 8 9 10 11 12 13 | penguins %>% head()# A tibble: 6 × 8 species island bill_length_mm bill_depth_mm flipper_length_mm body_mass_g <fct> <fct> <dbl> <dbl> <int> <int>1 Adelie Torgersen 39.1 18.7 181 37502 Adelie Torgersen 39.5 17.4 186 38003 Adelie Torgersen 40.3 18 195 32504 Adelie Torgersen NA NA NA NA5 Adelie Torgersen 36.7 19.3 193 34506 Adelie Torgersen 39.3 20.6 190 3650# <img draggable="false" role="img" class="emoji" alt=" |
" src="How to make a plot with ggplot2 using column name in a variable?
Let us say the column name of interest in a plot is saved in a variable. In the example below, our column name species is stored in a variable named “plot_this”
1 | plot_this <- "species" |
We are interested in making a boxplot with the column name in a variable on x-axis. If we naively try using the variable in a ggplot, we will not get the plot we need.
1 2 3 4 5 6 | penguins %>% ggplot(aes(x = plot_this, y = flipper_length_mm)) + geom_boxplot(outlier.shape = NA)+ geom_jitter(width=0.1)+ theme(legend.position = "none") |
Instead, we get a wrong plot as shown below.
Using tidy evaluation principles we can access the right data by using .data[[plot_this]] for the variable name of interest.
1 2 3 4 5 6 | penguins %>% ggplot(aes(x = .data[[plot_this]], y = flipper_length_mm))+ geom_boxplot(outlier.shape = NA)+ geom_jitter(width=0.1)+ theme(legend.position = "none") |
Now we get the boxplot with species on x-axis as we wanted.
Add colors to a plot with ggplot2 with a column name in a variable
If we want to add color to the boxplot, we will use the same approach with tidy evaluation. This time we will also use .data[[plot_this]] to specify the variable for coloring the boxplot.
1 2 3 4 5 6 7 | penguins %>% ggplot(aes(x = .data[[plot_this]], y = flipper_length_mm))+ #color = .data[[plot_this]])) + geom_boxplot(outlier.shape = NA)+ geom_jitter(width=0.1)+ theme(legend.position = "none") |
