use if else within ggplot chunk to change colour palette - r

Question

I'd like to be able to change the colour palette in ggplot2 boxplots, according to another variable data_origin.
This makes my boxplots, complete with legend:
library(hrbrthemes)
library(ggplot2)
library(reshape2)
library(tidyverse)
data_origin <- "airborne"
mytitle <- "something more than this"
legend_title <- "some words"
melted <- reshape2::melt(iris)
bp1 <- ggplot(melted, aes(x = variable, y = value, fill = Species)) +
geom_boxplot() +
theme_ipsum() +
scale_fill_brewer(palette = "Greens") +
theme(
legend.position = "bottom",
plot.title = element_text(size = 10)) +
theme(axis.text.x = element_blank()) +
ggtitle(mytitle) +
xlab("") +
ylab("") +
facet_wrap(~variable, scale = "free")
bp1
This however drops the legend completely and ignores the if else:
bp1 <- ggplot(melted, aes(x = variable, y = value, fill = Species)) +
geom_boxplot() +
theme_ipsum() +
scale_fill_brewer(legend_title, if (data_origin == "airborne" ) {palette = "Blues"} else {palette = "Greens"}) +
theme(
legend.position = "bottom",
# legend.title = legend_title,
plot.title = element_text(size = 10)) +
theme(axis.text.x = element_blank()) +
ggtitle(mytitle) +
xlab("") +
ylab("") +
facet_wrap(~variable, scale = "free")
bp1

Answer 1

Besides what #stefan suggested, there are two ways in which you can do this (that I know of). The first is using ifelse() (I moved the relevant part to the end):
data_origin <- "airborne"
bp1 <- ggplot(melted, aes(x = variable, y = value, fill = Species)) +
geom_boxplot() +
theme_ipsum() +
theme(
legend.position = "bottom",
# legend.title = legend_title,
plot.title = element_text(size = 10)) +
theme(axis.text.x = element_blank()) +
ggtitle(mytitle) +
xlab("") +
ylab("") +
facet_wrap(~variable, scale = "free") +
scale_fill_brewer(legend_title, palette = ifelse(
data_origin == "airborne",
"Blues",
"Greens"
))
bp1
The other one is to build the plot up in two steps:
data_origin <- "not airborne"
bp1 <- ggplot(melted, aes(x = variable, y = value, fill = Species)) +
geom_boxplot() +
theme_ipsum() +
theme(
legend.position = "bottom",
# legend.title = legend_title,
plot.title = element_text(size = 10)) +
theme(axis.text.x = element_blank()) +
ggtitle(mytitle) +
xlab("") +
ylab("") +
facet_wrap(~variable, scale = "free")
if (data_origin == "airborne") {
bp2 <- bp1 +
scale_fill_brewer(legend_title, palette = "Blues")
} else {
bp2 <- bp1 +
scale_fill_brewer(legend_title, palette = "Greens")
}
bp2
Created on 2021-08-01 by the reprex package (v2.0.0)