[R] Strange behavior when subsetting data frames with NAs

[Prof Brian D Ripley]

On Thu, 7 Mar 2002 apjaworski at mmm.com wrote:

>
> I guess I did not expect the change in row names for rows without NAs, that
> is the change from (1, 3) to (X1, X3) in my zz example.

It tells you this is a new set of row names, not just the old ones
repeated.

>
> Andy
>
> __________________________________
> Andy Jaworski
> Engineering Systems Technology Center
> 3M Center, 518-1-01
> St. Paul, MN 55144-1000
> -----
> E-mail: apjaworski at mmm.com
> Tel:  (651) 733-6092
> Fax:  (651) 736-3122
>
>
>
>                     Prof Brian D
>                     Ripley               To:     Andrzej P. Jaworski/US-Corporate/3M/US at 3M-Corporate
>                     <ripley at stats.o      cc:     r-help at stat.math.ethz.ch
>                     x.ac.uk>             Subject:     Re: [R] Strange behavior when subsetting data frames with NAs
>
>                     03/07/2002
>                     01:22 AM
>
>
>
>
>
>
>
> On Wed, 6 Mar 2002 apjaworski at mmm.com wrote:
>
> > 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
> >
> > I am not sure if this is bug or a feature, so I am reporting it here.
>
> What exactly do you find strange?  It is the correct behaviour and
> replicates that of S.  Remember that data frames have to have unique row
> names, and you asked for rows
>
> > zz[,2]>2
> [1]  TRUE FALSE  TRUE    NA    NA
>
> so new row names have to be created.  Matrices do not have to have unique
> dimnames.
>
> --
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272860 (secr)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>
>
>
>
>
>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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