R - Legend title or units when using Pheatmap

r heatmap pheatmap
alkey picture alkey · Apr 26, 2016 · Viewed 17.4k times · Source

I am using pheatmap to create a heatmap of values and would like to label the legend with the units of the z values in the matrix. In this example I would like the top of the legend to say Temperature [°C]. I have read the guidelines here for pheatmap, and it seems the only manipulation of the legend is to add a list of default numbers to be displayed in place of the scale. I cannot see any option to add a legend title per se.

Here is a generic block of code to generate a matrix and plot using pheatmap. I would really appreciate any advice on how to add a title to the legend. 

test <- matrix(rexp(200, rate=.1), ncol=20)
colnames(test) = paste("Room", 1:20, sep = "")
rownames(test) = paste("Building", 1:10, sep = "")

pheatmap(test, legend = TRUE, cluster_rows = FALSE, cluster_cols = FALSE)

enter image description here

Answer

Andrew J. Rech picture Andrew J. Rech · Sep 26, 2016

MikeyMike's answer is incredible; I also learned a lot by reading it.

However, I needed a dumb, ugly, 10 second solution:

test <- matrix(rexp(200, rate=.1), ncol=20)
colnames(test) = paste("Room", 1:20, sep = "")
rownames(test) = paste("Building", 1:10, sep = "")

pheatmap(test, legend_breaks = c(10, 20, 30, 40, max(test)), 
main = "", legend_labels = c("10", "20", "30", "40", "title\n"),
legend = TRUE, cluster_rows = FALSE, cluster_cols = FALSE)

Which produces this heatmap:

enter image description here

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