ggplot2 heatmap with fixed scale colorbar between graphs

Question

I need to draw 3 different plots setting the same scale range color. I have 3 matrices with different range of values.

For example:

range(matrixA) 
# 0.60 0.85  
range(matrixB) 
# 0.65 0.95  
range(matrixA) 
# 0.5 1.0

I would like to have the same color fill for the plots. For example, for all 0.8 value in the difference plots, if in the first plot 0.8 orange, I want all 0.8 value in different graphs to be the same orange.

My problem in this moment is:

In the first plot, the color of the max value is red, then the value 0.85 is red.

In the second plot, the max value is red but in this case the max value is 0.95 and the problem arises.

My code:

mat.melted <- melt(matrixA)
colnames(mat.melted) <- c("p","c","v")
p <- ggplot(mat.melted, aes(x=c,y=p,fill=v) + 
         geom-tile() + 
         scale_fill_gradintn(limits = c(min(as.vector(matrixA)), max(as.vector(matrixA))), 
                             colors = c("yellow","orange","red"))

Answer 1

You need to set the same range (limits of color bar) for all of them and also specify the colors.

rng = range(matrixA, matrixB, matrixC)

And add this to your ggplot code:

g + scale_fill_gradient2(low="green", mid="lightblue", high="red", #colors in the scale
               midpoint=mean(rng),    #same midpoint for plots (mean of the range)
               breaks=seq(0,1,0.25), #breaks in the scale bar
               limits=c(floor(rng[1]), ceiling(rng[2])))

Example:

Below is an example that helps you to get what you want:

x <- matrix(60:85, 5)/100
y <- matrix(65:95, 5)/100
z <- matrix(50:100, 5)/100


rng = range(c((x), (y), (z)))

library(reshape)
library(ggplot2)

ggplot(data = melt(x)) + geom_tile(aes(x=X1,y=X2,fill = value)) +
  scale_fill_gradient2(low="green", mid="lightblue", high="red", #colors in the scale
                   midpoint=mean(rng),    #same midpoint for plots (mean of the range)
                   breaks=seq(0,1,0.25), #breaks in the scale bar
                   limits=c(floor(rng[1]), ceiling(rng[2]))) + #same limits for plots
                   ggtitle("X")

ggplot(data = melt(y)) + geom_tile(aes(x=X1,y=X2,fill = value)) +
  scale_fill_gradient2(low="green", mid="lightblue", high="red", 
                   midpoint=mean(rng),   
                   breaks=seq(0,1,0.25), 
                   limits=c(floor(rng[1]), ceiling(rng[2]))) +
                    ggtitle("Y")                  
  
ggplot(data = melt(z)) + geom_tile(aes(x=X1,y=X2,fill = value)) +
 scale_fill_gradient2(low="green", mid="lightblue", high="red", 
                   midpoint=mean(rng),    
                   breaks=seq(0,1,0.25), 
                   limits=c(floor(rng[1]), ceiling(rng[2]))) +
                    ggtitle("Z")   

This will give you: