yes it is.
and a correlation of 0 isn't exactly white (#FFFFFF) either.
have a look at the panel.pie function.
the crucial part is
ncol <- 14
pal <- col.corrgram(ncol)
col.ind <- round(ncol * (corr + 1)/2)
so an correlation near -1 maps to an index 0, which isn't a proper index
in R.
Alter these lines to
ncol <- 15 #so 0 becomes "#FFFFFF"
pal <- col.corrgram(ncol)
col.ind <- round((ncol-1) * (corr + 1)/2)+1
hth.
Am 28.06.2011 13:11, schrieb Niels Janssen:
> Dear list,
>
> I have a problem with the "corrgram" function. It does not seem to
> "color" large negative correlations, while the same correlation, if
> positive, provides no problems. Is this a bug?
>
> require(corrgram)
> a = seq(1,100)
> b = -jitter(seq(1,100), 80)
> cor(a,b) # r about -.96
> c=as.data.frame(cbind(a,b))
> corrgram(c, order=NULL, lower.panel=panel.pie,upper.panel=NULL,
> text.panel=panel.txt) # no color
>
> c$b = -1*c$b # flip direction of correlation
> cor(c$a, c$b) # r now about +.96
> corrgram(c, order=NULL, lower.panel=panel.pie,upper.panel=NULL,
> text.panel=panel.txt) #no problem with color.
>
> Thanks!
>
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--
Eik Vettorazzi
Department of Medical Biometry and Epidemiology
University Medical Center Hamburg-Eppendorf
Martinistr. 52
20246 Hamburg
T ++49/40/7410-58243
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