How to add colorbar with perspective plot in R

Question

May be it is very simple to do, but after hours of searching I didn\'t able to find how to add colorbar beside the persp plot using R. Could anyone kindly help? Thanks.

Answer 1

It's possible to add a legend using image.plot in the fields package. Using an example from ?persp:

library(fields)

## persp example code
par(bg = "white")
x <- seq(-1.95, 1.95, length = 30)
y <- seq(-1.95, 1.95, length = 35)
z <- outer(x, y, function(a, b) a*b^2)
nrz <- nrow(z)
ncz <- ncol(z)
# Create a function interpolating colors in the range of specified colors
jet.colors <- colorRampPalette( c("blue", "green") )
# Generate the desired number of colors from this palette
nbcol <- 100
color <- jet.colors(nbcol)
# Compute the z-value at the facet centres
zfacet <- (z[-1, -1] + z[-1, -ncz] + z[-nrz, -1] + z[-nrz, -ncz])/4
# Recode facet z-values into color indices
facetcol <- cut(zfacet, nbcol)
persp(x, y, z, col = color[facetcol], phi = 30, theta = -30, axes=T, ticktype='detailed')

## add color bar
image.plot(legend.only=T, zlim=range(zfacet), col=color)

EDIT thanks to @Marc_in_the_box: the range of the colorbar is defined by zfacet, not by z

Answer 2

persp has a tricky way of computing colors based on the mid points of the facets. This makes your work a bit difficult in extracting the color levels, but I think I have found a way. In any case, layout is probably your best bet for splitting your device and adding a color bar:

Example:

layout(matrix(1:2, nrow=1, ncol=2), widths=c(4,1), heights=1)
par(bg = "white", mar=c(4,4,1,1))
x <- seq(-1.95, 1.95, length = 30)
y <- seq(-1.95, 1.95, length = 35)
z <- outer(x, y, function(a, b) a*b^2)
nrz <- nrow(z)
ncz <- ncol(z)
# Create a function interpolating colors in the range of specified colors
jet.colors <- colorRampPalette( c("blue", "green") )
# Generate the desired number of colors from this palette
nbcol <- 100
color <- jet.colors(nbcol)
# Compute the z-value at the facet centres
zfacet <- (z[-1, -1] + z[-1, -ncz] + z[-nrz, -1] + z[-nrz, -ncz])/4
# Recode facet z-values into color indices
facetcol <- cut(zfacet, nbcol)
persp(x, y, z, col = color[facetcol], phi = 30, theta = -30)

labs <- levels(facetcol)
tmp <- cbind(lower = as.numeric( sub("\\((.+),.*", "\\1", labs) ),
      upper = as.numeric( sub("[^,]*,([^]]*)\\]", "\\1", labs) ))

par(mar=c(10,0,10,5))
image(x=1, y=rowMeans(tmp), matrix(rowMeans(tmp), nrow=1, ncol=nbcol), col=color, axes=FALSE, xlab="", ylab="")
axis(4)
box()

btw, I realized that the last example from persp looks to have an error in it's calculation of facet values - as is, they are the sum of the corner values, and need to be divided by 4 in order to use them directly in extracting the color break points:

# Compute the z-value at the facet centres
zfacet <- z[-1, -1] + z[-1, -ncz] + z[-nrz, -1] + z[-nrz, -ncz]
# Recode facet z-values into color indices
facetcol <- cut(zfacet, nbcol)

#should be:
# Compute the z-value at the facet centres
zfacet <- (z[-1, -1] + z[-1, -ncz] + z[-nrz, -1] + z[-nrz, -ncz]) / 4
# Recode facet z-values into color indices
facetcol <- cut(zfacet, nbcol)