> I'm trying to draw a 2D plot using multiple tints of red. The
> (simplified) setup is the following: || year | x | y ||
You might find this function useful:
map_colour_gradient <- function(x, low="red",
mid="white",high="black", midpoint = 0) {
x <- as.numeric(x)
low.rgb <- col2rgb(low, TRUE)/256
mid.rgb <- col2rgb(mid, TRUE)/256
high.rgb <- col2rgb(high, TRUE)/256
interp_r <- approxfun(c(min(x, na.rm=TRUE), midpoint, max(x,
na.rm=TRUE)), c(low.rgb[1], mid.rgb[1], high.rgb[1]))
interp_g <- approxfun(c(min(x, na.rm=TRUE), midpoint, max(x,
na.rm=TRUE)), c(low.rgb[2], mid.rgb[2], high.rgb[2]))
interp_b <- approxfun(c(min(x, na.rm=TRUE), midpoint, max(x,
na.rm=TRUE)), c(low.rgb[3], mid.rgb[3], high.rgb[3]))
rgb(interp_r(x), interp_g(x), interp_b(x))
}
Given a numeric vector x, it will create a smooth gradient (linearly
through RGB space).
eg.
x <- rnorm(100)
y <- rnorm(100)
plot(x, y, col=map_colour_gradient(x), pch=20)
plot(x, y, col=map_colour_gradient(x, low="black", high="black",
mid="yellow"), pch=20)
Note, however, using colour is only likely to find the most prominent
of patterns.
Hadley
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