# R/Contour Plots

From QERM Wiki

# Contour Plots

R has two built-in functions for contour plots, contour, and filled.contour. Examples of their use can be seen from the code below:

x <- 1:50 y <- 1:70 z <- matrix(expand.grid(x,y)$Var1^2 + expand.grid(x,y)$Var2^2,50,70) # plain contour(x,y,z) # adjusting levels mylevels <- seq(0,7500,500) contour(x,y,z,levels=mylevels,xaxs='i',yaxs='i') # filled contours filled.contour(x,y,z,color.palette=heat.colors) filled.contour(x,y,z,col=grey(seq(0,1,length=length(mylevels)))) # add this to line above and see bad match contour(x,y,z,levels=mylevels,add=T)

However, it can be frustrating to realize that the way filled.contour was implemented does not allow removing the key or overplotting with lines and labels. To realize this, try the following:

filled.contour(x,y,z,col=grey(seq(0,1,length=length(mylevels)))) # add this to line above and see bad match contour(x,y,z,levels=mylevels,add=T)

A solution is to use the modified function, filled.contour2, as follows

# filled.contour function modified to not have key filled.contour2(x,y,z,col=grey(seq(0.3,1,length=length(mylevels)))) # now we can successfully add lines and values contour(x,y,z,levels=mylevels,add=T)

Download the modified function filled.contour2.R

Better yet, Carey McGilliard and Bridget Ferris made further modifications to allow multiple filled contours per page and the addition of the legend on the side to makes figures like the one at right. filled.contour3.R filled.legend.R