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-   -   heatmap and heatmap.2 (http://seqanswers.com/forums/showthread.php?t=20935)

capricy 06-18-2012 06:17 PM

heatmap and heatmap.2
 
I plot the same set of data with heatmap and heatmap.2 respectively, and got distinctly different profiles. Anybody could explain this? I know heatmap.2 has extra functions, such as color key; but it looks that its imaging algorithm might also be quite different from heatmap. Is it true? Thanks.

rboettcher 06-19-2012 05:02 AM

I noticed the same thing some time ago...

heatmap does not use the same colorkey for every row by default. Instead it performs some weird scaling...
This essentially means that the rows are NOT comparable by means of colour, since the scaling is performed independently for every row.

you can try this very easily with the following commands:

x = c(1:10)
a = cbind(x,x,x,x)
a[1,2] = 100
a[1,3] = 1000
heatmap(a)


Here's what the help says:
"By default (scale = "row") the rows are scaled to have mean zero and standard deviation one. There is some empirical evidence from genomic plotting that this is useful. "

set scale = "none" and your results will be comparable.

heatmap(a,scale="none")
heatmap.2(a,trace="none")

Best regards,
René

capricy 06-20-2012 06:47 AM

Thanks for help:)


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