2 color heatmap in R with middle color anchored to a specific value

Question

This heatmap image was generated in Excel but as I'm trying to learn R I would like to know how to make a heatmap like that with R.

Right now, this code is working but not as it was supposed to...

(p <- ggplot(melt(heat), aes(Var2, Var1))
 + geom_tile(aes(fill = value), colour = "white")
 + scale_fill_gradient(low = "red", high = "green"))

I would like to have 2 gradients, green(highest value) to white (the number 1000) to red(lowest value). Is it possible in R?

heat dataset:

> heat[0:10,0:10]
          [,1]     [,2]      [,3]      [,4]      [,5]      [,6]      [,7]      [,8]      [,9]     [,10]
 [1,] 1000.000    0.000    0.0000    0.0000  757.0317  709.3896  843.7676  932.2801    0.0000 1016.7203
 [2,] 1087.658 1000.000    0.0000    0.0000  935.5829  854.5110  889.5042 1091.4610  929.1611    0.0000
 [3,] 1181.599 1361.953 1000.0000    0.0000    0.0000 1102.1590 1147.1300  984.1374  969.0718 1058.3456
 [4,] 1319.012 1405.954 1187.5215 1000.0000    0.0000 1093.8854 1195.7298 1077.0797 1119.4640 1159.5207
 [5,]    0.000    0.000  909.1927  817.5097 1000.0000    0.0000 1101.2891 1064.6516 1037.1623  990.3974
 [6,]    0.000    0.000    0.0000    0.0000  887.7498 1000.0000 1015.9835 1062.1668 1105.2163  983.2319
 [7,]    0.000    0.000    0.0000    0.0000    0.0000    0.0000 1000.0000  911.0699 1026.1989  951.3572
 [8,]    0.000    0.000    0.0000    0.0000    0.0000    0.0000    0.0000 1000.0000  834.8725  927.6802
 [9,] 1261.824    0.000    0.0000    0.0000    0.0000    0.0000    0.0000    0.0000 1000.0000  795.6285
[10,]    0.000 1121.210    0.0000    0.0000    0.0000    0.0000    0.0000    0.0000    0.0000 1000.0000

Answer 1

You can use ?scale_fill_gradientn

gving you values:

  library(scales)
  heat.dat <- heat[0:10,0:10]
  dat <- expand.grid(var1=1:10, var2=1:10)
  dat$value <- melt(heat.dat)$value
  ggplot(dat, aes(x=var1,y=var2))+ 
        geom_tile(aes(fill = value),colour='white')+
        scale_fill_gradientn(colours=c("red","white","green"),
         values  = rescale(c(min(dat$value), 1000, max(dat$value)))

Using Lattice:

with(dat,
levelplot(round(value,0)~y*x, 
          dat, 
          panel=function(...) {
                 arg <- list(...)
                 panel.levelplot(...)
                 panel.text(arg$x, arg$y,arg$z)},
          scales = list(y = list(at=y,labels=y),
                        x = list(at=y,labels=y)),
          col.regions = colorRampPalette(c("red", "white", "green"),interpolate ='spline'))
)