On Sep 28, 2012, at 3:16 PM, Nick Fankhauser wrote:
> Hello R-Users!
>
> I'm using a heatmap to visualize a matrix of values between -1 and 3.
> How can I set the colors so that white is zero, below zero is blue of
> increasing intensity towards -1 and above zero is red of increasing intensity
> towards red?
>
> I tried like this (using the marray and gplots packages from bioconductor):
> mcol <- maPalette(low="blue", mid="white", high="red",k=100)
> heatmap.2(my_matrix, col=mcol)
>
> But white does not correspond to zero, because the value distribution is not
> symmetrical, so that zero is not in the middle.
> Is it somehow possible to create a color palette with white centered at zero?
The way you stated it at the beginning, I thought you should want the palette
centered at 1 rather than 0:
test <- seq(-1,3, len=20)
shift.BR <- colorRamp(c("blue","white", "red"), bias=2)((1:16)/16)
tpal <- rgb(shift.BR, maxColorValue=255)
barplot(test,col = tpal)
Perhaps I was being led astray by a somewhat similar question on StackOverflow.
--
David Winsemius, MD
Alameda, CA, USA
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