Strange behavior when subsetting data frames with NAs

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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