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Set Individual Color Scheme for groups of facet panels + ggplot2 + facet_wrap

August 7, 2023

I am trying to assign groups of facet panels individual color schemes using ggplot 2. In the below example my goal is that A and B would have the same pallet, C would have a different pallet, and D and E would have the same pallet.

# Number of IDs
n_ids <- 10 

# Generate IDs
ids <- paste0("ID_", 1:n_ids)

# Number of periods per ID
n_periods <- 3

# Generate periods
periods <- rep(c("P1", "P2", "P3"), each = n_ids)

# Number of categories 
n_cats <- 5 

# Generate categories
categories <- rep(LETTERS[1:n_cats], times = n_ids * n_periods)

# Generate values
values <- rnorm(n_ids * n_periods * n_cats, 100, 15)

# Assemble into dataframe
df <- data.frame(ID = ids, 
                 Period = periods,
                 Category = categories,
                 Value = values)

# Plot
p <- ggplot(df, aes(x=Period, y=Value, fill=Period)) +
  geom_boxplot() +
  geom_jitter(width=0.2,alpha=0.4, size=1) +
  facet_wrap(~Category, ncol=6, scales='free') +
  labs(title="Repetitive Behavior Score", x="Group", y="Value")

# Color vector
colors <- c("#1F78B4", "#E69F00", "#33A02C", "#FB9A99")

# Map colors to categories
color_map <- c(
  "A" = "#1F78B4",
  "B" = "#1F78B4",
  
  "C" = "#E69F00",
  
  "D" = "#33A02C",
  "E" = "#33A02C"
)

# Set fill scale
p + 
  scale_fill_manual(values = color_map)

but they are all just returning gray… has anybody tried this before? I know it can be done with scale_fill and scale_color but I can’t find examples for facet panels.

>Solution :

You could map the fill aesthetic to the interaction of your x axis and faceting variables. The downside is that you need to specify colors manually.

ggplot(df, aes(Period, Value, fill = interaction(Period, Category))) +
  geom_boxplot() +
  geom_jitter(width = 0.2, alpha = 0.4, size = 1) +
  facet_wrap(~Category, ncol = 6, scales = 'free') +
  labs(title = "Repetitive Behavior Score", x = "Group", y =" Value") +
  scale_fill_manual(values = c(rep(c("red4", "green4", "blue4"), 2),
                               c("hotpink", "orange", "dodgerblue"),
                               rep(c("purple3", "beige", "gray80"), 2)),
                    guide = guide_none()) +
  jtools::theme_apa()