Suppress warnings for color brewer palettes with <3 colors

[wch]

This suppresses warnings when <3 colors are requested, but keeps them when more colors are requested than the palette contains.

[hadley]

Doesn't scales give it's own warning in some circumstances?

[wch]

I'm not sure what you have in mind - this will only suppress warnings from brewer.pal. Looking at the code for brewer.pal, it gives warnings in two circumstances: too few, and too many colors requested. It throws an error when a non-existent palette is requested:

> brewer.pal
function (n, name) 
{
    if (!(name %in% namelist)) {
        stop(paste(name, "is not a valid palette name for brewer.pal\n"))
    }
    if (n < 3) {
        warning("minimal value for n is 3, returning requested palette with 3 different levels\n")
        return(brewer.pal(3, name))
    }
    if (n > maxcolors[which(name == namelist)]) {
        warning(paste("n too large, allowed maximum for palette", 
            name, "is", maxcolors[which(name == namelist)]), 
            "\nReturning the palette you asked for with that many colors\n")
        return(brewer.pal(maxcolors[which(name == namelist)], 
            name))
    }

...

The rest of the code in the function just contains palettes. So I think this patch safely suppresses warnings.

[hadley]

I think I was getting confused with old ggplot2 code - it looks good.