ggplot2 scale fill gradient with discrete cap

Question

I am looking to have a heat map of values. I want the heat map to go from blue for low values (0 in my sample code) to green for high values (75 in my sample code). However, the data contains values greater than 75. I want any values greater than 75 to be filled in red.

So to summarize, I want the fill to be scaled from 0 top 75 in blue to green with any value greater than 75 filled in red. The code I have now sort of does this, but still scales from green to red in values from 76-100 rather than have them all be red.

I have used the answer from Brian Diggs in the post (ggplot2 heatmap with colors for ranged values), but that answer does not cover what to do with filling all values beyond a cap value for a gradient scale.

The post (ggplot geom_point() with colors based on specific, discrete values) seems to answer a very similar question for geom_point, but I am having trouble adapting it to geom_tile.

My sample code is below and any help is appreciated!

#Check packages to use in library
{
  library('ggplot2')
  library('scales')
}

#Data

horizontal_position <- c(-2, -1, 0, 1, 2)
vertical_position <- c(-2, -2, -2, -2, -2, -1, -1, -1, -1, -1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2)
data_val <- sample(0:100, 25)
all_data <-data.frame(horizontal_position, vertical_position, data_val)

     all_data %>%
      ggplot(aes(horizontal_position, vertical_position)) +
      geom_tile(aes(fill = data_val), colour = "transparent") + 
      geom_text(aes(label = data_val),colour="white")+
      scale_fill_gradientn(colours = c("blue", "lightblue", "lightgreen", "green", "red"),
                           breaks=c(0,25,50,75,Inf),
                           guide = "colorbar")

Brian Brian · Accepted Answer · 2017-04-26T19:13:33

Here's a partial solution, which colors the figure but leaves the legend not entirely correct:

all_data %>% 
  mutate(val2 = replace(data_val, data_val > 75, NA)) %>% 
  ggplot(aes(horizontal_position, vertical_position)) +
  geom_tile(aes(fill = val2), colour = "transparent") + 
  geom_text(aes(label = data_val),colour="white")+
  scale_fill_gradientn(colours = c("blue", "lightblue", "lightgreen", "green"),
                       breaks=c(0,25,50,75,Inf),
                       na.value = "red")

The trick is setting your out-of-bounds values to NA, which has a special optional value in most of the aesthetic scales. Of course, this breaks down if your actual data have true NAs, and as I mentioned, getting it to show up in the colorbar is another quagmire.

Edited to add: a quick search brought up some solutions: Add a box for the NA values to the ggplot legend for a continous map

ggplot2 scale fill gradient with discrete cap

1 Answers