Non-linear color distribution over the range of values in a geom_raster

Question

I'm faced with the following problem: a few extreme values are dominating the colorscale of my `geom_raster` plot. An example is probably more clear (note that this example only works with a recent ggplot2 version, I use 0.9.2.1): ``` library(ggplot2) library(reshape) theme_set(theme_bw()) m_small_sd = melt(matrix(rnorm(10000), 100, 100)) m_big_sd = melt(matrix(rnorm(100, sd = 10), 10, 10)) new_xy = m_small_sd[sample(nrow(m_small_sd), nrow(m_big_sd)), c("X1","X2")] m_big_sd[c("X1","X2")] = new_xy m = data.frame(rbind(m_small_sd, m_big_sd)) names(m) = c("x", "y", "fill") ggplot(m, aes_auto(m)) + geom_raster() + scale_fill_gradient2() ``` Right now I solve this by setting the values over a certain quantile equal to that quantile: ``` qn = quantile(m$fill, c(0.01, 0.99), na.rm = TRUE) m = within(m, { fill = ifelse(fill < qn[1], qn[1], fill) fill = ifelse(fill > qn[2], qn[2], fill)}) ``` This does not really feel like an optimal solution. What I would like to do is have a non-linear mappi…

Accepted Answer

Seems that ggplot (0.9.2.1) and scales (0.2.2) bring all you need (for your original `m`):

```
library(scales)

qn = quantile(m$fill, c(0.01, 0.99), na.rm = TRUE)
qn01 <- rescale(c(qn, range(m$fill)))

ggplot(m, aes(x = x, y = y, fill = fill)) + 
   geom_raster() + 
   scale_fill_gradientn (
      colours = colorRampPalette(c("darkblue", "white", "darkred"))(20),
      values = c(0, seq(qn01[1], qn01[2], length.out = 18), 1)) +
   theme(legend.key.height = unit (4.5, "lines"))
```

Non-linear color distribution over the range of values in a geom_raster

Solution

Problem