Plot zeros in a different colour to colour scale in ggplot2

May 10, 2022

I have a data frame, df:

df <- structure(list(animal = c("cat", "cat", "cat", "cat", "cat", 
"cat", "cat", "cat", "cat", "cat", "cat", "cat", "cat", "cat", 
"cat", "cat", "cat", "cat"), id = c("201", "202", "203", "204", 
"215", "217", "201", "202", "203", "204", "215", "217", "201", 
"202", "203", "204", "215", "217"), tissue = c("tail", "tail", 
"tail", "tail", "tail", "tail", "whiskers", "whiskers", "whiskers", 
"whiskers", "whiskers", "whiskers", "feet", "feet", "feet", "feet", 
"feet", "feet"), value = c(0.5, 2.2, 0, 0.2, 0, 0, 2.8, 19.9, 
0, 85, 0, 0, 1.9, 4.1, 0, 0.4, 0, 120)), row.names = c(NA, -18L
), class = "data.frame")

head(df)
  animal  id tissue value
1    cat 201   tail   0.5
2    cat 202   tail   2.2
3    cat 203   tail   0.0
4    cat 204   tail   0.2
5    cat 215   tail   0.0
6    cat 217   tail   0.0

I have the following plotting function:

p <- ggplot(df, aes_string(x = "id", y = "tissue", fill = "value")) +
    geom_tile(color = "white") +
    geom_text(aes_string(label = "value"), color = "black", size = 2) +
    scale_fill_gradient(
        low = "white", high = "red", na.value = "#D0D0D0") +
    theme(axis.text.x = element_text(angle = 90, vjust = 0.5, hjust=1))

This produces:

I would like the zero values to be plotted in white, but any value above zero to start from an off-red (eg. #FEECE3).

I have tried this:

p <- ggplot(df, aes_string(x = "id", y = "tissue", fill = "value")) +
    geom_tile(color = "white") +
    geom_text(aes_string(label = "value"), color = "black", size = 2) +
            scale_fill_gradient2(
                low = "white", mid = "#FEECE3", high = "red", na.value = "#D0D0D0",
                midpoint = 1) +
    theme(axis.text.x = element_text(angle = 90, vjust = 0.5, hjust=1))

But it plots the zeros in the off-red colour.

How can I get just the zeros to plot in white?

>Solution :

You could use scale_fill_gradientn. Set your three colours to white, off-white and red, and set the values at which they reach these colors as 0, the smallest possible non-zero number, and 1.

ggplot(df, aes_string(x = "id", y = "tissue", fill = "value")) +
  geom_tile(color = "white") +
  geom_text(aes_string(label = "value"), color = "black", size = 2) +
  scale_fill_gradientn(colours = c('white', "#FEECE3", 'red'),
                       values = c(0, .Machine$double.eps, 1)) +
  theme(axis.text.x = element_text(angle = 90, vjust = 0.5, hjust=1))