[R] Re: Strange behavior when subsetting data frames with NAs
Gary Collins
gco at eortc.be
Thu Mar 7 08:02:04 CET 2002
>Here is what I get using R 1.4.1 on Win2k (using precompiled version from
>CRAN) and RH 7.2 Linux (compiled form source):
> > data.frame(a=c(1, 2, 3, NA, NA), b=c(3, 1, 3, NA, NA)) -> zz
> > zz[zz[,2]>2, ]
> a b
> X1 1 3
> X3 3 3
> NA NA NA
> NA1 NA NA (if there are more
>rows with NAs, I get consecutive labels NA2, NA3, ...)
> > zz1 <- na.omit(zz)
> > zz1[zz1[,2]>2, ]
> a b
> 1 1 3
> 3 3 3
>
> also
> > as.matrix(zz) -> zz
> > zz[zz[,2]>2, ]
> a b
> 1 1 3
> 3 3 3
> NA NA NA
> NA NA NA
in the second case, you have not done an na.omit() operation, that you did
in the case of the data.frame.
So if you did
> na.omit(zz[zz[,2]>2,])
a b
X1 1 3
X3 3 3
This compares to the data.frame operation.
> I am not sure if this is bug or a feature, so I am reporting it here.
>Andy
__________________________________________________
Gary S. Collins, PhD,
Statistics Research Fellow,
Quality of Life Unit,
European Organisation for Research and Treatment of Cancer,
EORTC Data Center,
Avenue E. Mounier 83, bte. 11,
B-1200 Brussels, Belgium.
Tel: +32 2 774 1 606
Fax: +32 2 779 4 568
http://www.eortc.be/home/qol/
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