[R] Plotcorr: colour the ellipses to emphasize the differences

Uwe Ligges ligges at statistik.uni-dortmund.de
Sun Oct 17 15:21:07 CEST 2004

Gorjanc Gregor wrote:

> Hello R users!
> I began with R and I must say that it is really nice. I have data with a lot of variables
> and have a problem to extract the pattern from correlation matrix. So I tried with plotcorr
> and it went fine. While I was reading the help page of this function, I found that ellipse
> display can be even better with use of different colors (the code is bellow). However I have
> a problem to understand the process of generating the colors. The function cm.colors() with argument 11 produces scale of colors with 11 points. What is the meaning of [5*xc + 6])? If I ommit this part from the code, I see that ellipses bellow diagonal do not have the same color as above the diagonal. In given example numbers 5 and 6 are given (I think so) since there are 11 variables in dataset mtcars. 
> How can one use this setup for other datasets? For example I have a dataset with 15 variables.
> I would also like to know if it is possible to use some other scale of colors instead of cm.colors, rainbow, heat.colors, terrain.colors, topo.colors. I would like to have positive correlations in blue and nagative ones in red spectrum of colors. Is it possible?

Have you looked at the RColorBrewer package?

Uwe Ligges

> Thank you!
> # Colour the ellipses to emphasize the differences
> corr.mtcars <- cor(mtcars)
> ord <- order(corr.mtcars[1,])
> xc <- corr.mtcars[ord, ord]
> plotcorr( xc, col=cm.colors(11)[5*xc + 6])
> With regards, Lep pozdrav
>     Gregor GORJANC
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