heatmap in ggplot, different color for each group - r

Question

I am trying to produce a heatmap in ggplot. I want each group to have different color gradient, but don't know how to do that. My current code looks like this:
## dummy data -----------------------------------------------------------------------------
data <- data.frame(
group = sample(c("Direct Patient Care", "Indirect Patient Care", "Education", "Rounds", "Handoff", "Misce"), 30, replace = T),
pct = rnorm(30, mean = 50, sd = 8)
)
## generate group id
data <- data %>%
group_by(group) %>%
mutate(id = row_number())
data$grpid <- with(data, ifelse(group == "Direct Patient Care", 1, ifelse(group == "Indirect Patient Care", 2,
ifelse(group == "Education", 3,
ifelse(group == "Rounds", 4,
ifelse(group == "Handoff", 5,6 ))))))
## draw graph ------------------------------------------------------------------------------
library(ggplot2)
p <- ggplot(data, aes(x=id, y=group, fill = pct)) +
theme(panel.background = element_rect(fill = "white", colour = "grey50"), aspect.ratio = 0.4) +
theme(panel.grid.major = element_blank(),
panel.grid.minor = element_blank()
)+
# guides(fill = guide_legend("Time, %")) +
geom_tile() +
scale_x_continuous (name = " ", breaks = seq(1, 8, by = 1)) +
scale_y_discrete(name = " ") +
theme(axis.text.x = element_text(angle = 0,hjust = 1,vjust = 1), plot.title = element_text(hjust = 0.5) ) +
ggtitle("Heatmap of time spent doing activities across 194 shifts")
p + scale_fill_gradient2(low = "white", high = "red", limits = c(0, 80), breaks = c(0, 10, 20, 30, 40, 50, 60, 70), guide = guide_legend("Time, %")) ## change the color theme ##
And the resulting figure looks like this:
How can I change the color theme for each group, like red for 'Rounds', blue for 'Misce', green for 'Handoff' etc...
Many thanks!

Answer 1

You can do this by creating your own rescaled value in your data and then slightly "hacking" the alpha aesthetic combined with the fill aesthetic:
library(tidyverse)
data %>%
group_by(group) %>%
mutate(rescale = scales::rescale(pct)) %>%
ggplot(., aes(x = factor(id), y = group)) +
geom_tile(aes(alpha = rescale, fill = group), color = "white") +
scale_alpha(range = c(0.1, 1))
First we create a new column called rescale which rescales the pct from 0 to 1 then you force the scale_alpha(range = c(0, 1)) [note, in this case I used c(0.1, 1) so that you can still "see" the zero points.
Finally, you probably want to remove the guides:
data %>%
group_by(group) %>%
mutate(rescale = scales::rescale(pct)) %>%
ggplot(., aes(x = factor(id), y = group)) +
geom_tile(aes(alpha = rescale, fill = group), color = "white") +
scale_alpha(range = c(0.1, 1)) +
theme(legend.position = "none")
N.B. by using aes(x = factor(id)... you can get around manually setting your x-axis since in this case it appears you want to treat it as a factor not a numeric scale.
Finally, if you really want to get fancy, you could double-encode the axis.text.y colors to that of the levels of your factor (i.e., data$group) variable:
data %>%
group_by(group) %>%
mutate(rescale = scales::rescale(pct)) %>%
ggplot(., aes(x = factor(id), y = group)) +
geom_tile(aes(alpha = rescale, fill = group), color = "white") +
scale_alpha(range = c(0.1, 1)) +
theme(legend.position = "none",
axis.text.y = element_text(color = scales::hue_pal()(length(levels(data$group)))),
axis.ticks = element_blank()) +
labs(x = "", y = "")