[BioC] VSN 2.2
Hans-Ulrich Klein
h.klein at uni-muenster.de
Thu May 3 15:50:40 CEST 2007
Hi all,
I noticed that the function "vsn2" is much slower than the function
"vsn". Probably it is not a general problem, but at least for my dataset
the difference in computation time is remarkable:
> vsnResG <- vsn(RG$G[subSet,1:5], strata=RG$genes$Block[subSet]);
vsn: 25727 x 5 matrix (48 strata). 100% done.
Finished after ~30s.
> vsnFitG <- vsn2(RG$G[subSet,1:5], strata=RG$genes$Block[subSet])
vsn: 25727 x 5 matrix (48 strata). 100% done.
Finished after ~1h.
After transformation
> Gvsn_new <- predict(vsnFitG, RG$G[subSet,1:5])
> parsG <- preproc(description(vsnResG))$vsnParams
> Gvsn_old <- vsnh(RG$G[subSet,1:5] + 0, parsG,
strata=RG$genes$Block[subSet])
I checked that the variance is independet of the mean. And plotted the
new versus the old glog intensities:
> plot(Gvsn_new, Gvsn_old/log(2), pch=".")
> abline(0,1, col="red")
Here, the plot shows a couple of "stripes" with slope 1 and different
intercepts.
I uploaded the plot:
http://img504.imageshack.us/img504/4700/oldnewglogge0.png
I guess that the "stripes" are the 48 printtips (used to stratify the
data). Thus, the different additive offsets should not influence further
analysis (like limma).
Best wishes,
Hans-Ulrich
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