[R] documentation inconsistency for [.data.frame ?

[ripley@stats.ox.ac.uk]

On Tue, 4 Jun 2002, Tony Plate wrote:

> (Using R1.5.0 patched for Windows)
> Subscripting rows of data.frame only sometimes does what the documentation
> says:
>
> >      When `[.data.frame' is used for subsetting rows of a `data.frame',
> >      it returns a dataframe with unique row names, using `make.names( *
> >      , unique = TRUE)', see the `swiss' example below.
>
> Row names seem to be modified in this way only when row indices pick out
> non-existing or non-unique rows.

Right, and that's exactly what it says.  The rownames in a data frame
started out as unique and non-missing, and those are the ways that you
can break that.

I think you are mis-reading the sentence.

> Splus6.0 for Windows has similar behavior, though the details are different
> (modification of row names is triggerred only by non-unique indices,
> including zeros, in Splus).  However, at least the R documentation does say
> *something* about row names being modified by make.names.

Well, that system does not have missing character strings, so the rule is
slightly different.

> [Personally, I'd rather have a version of the dataframe class whose methods
> didn't go around modifying the row and column names I had assigned...]

Impossible.  Unique row names are part of the class definition.  If you
insist on using operations that violate that, you should expect to be
corrected.

> Note that the documentation could be considered correct if it is assumed
> that the documentation only applies in the cases where the input data frame
> has row names that are syntactically valid variable names (i.e., will pass
> through make.names() untouched).  However, I couldn't find anything in R or
> S-plus online documentation that said this is a requirement for data frames.

It is a requirement that they be unique.  It is not a requirement that
they be syntactically valid.  The latter is just how R corrects your
mistakes.

>  > data.frame(x=1:3,y=4:6,row.names=c("3AB","C/D","E.F"))[c(1,2,3),]
>      x y
> 3AB 1 4
> C/D 2 5
> E.F 3 6
>  > data.frame(x=1:3,y=4:6,row.names=c("3AB","C/D","E.F"))[c(1,2,3,NA),]
>        x  y
> X3AB  1  4
> C.D   2  5
> E.F   3  6
> NA   NA NA
>  > data.frame(x=1:3,y=4:6,row.names=c("AB","C/D","E.F"))[c(1,2,3,0),]
>      x y
> AB  1 4
> C/D 2 5
> E.F 3 6
>  > data.frame(x=1:3,y=4:6,row.names=c("AB","C/D","E.F"))[c(1,2,3,4),]
>       x  y
> AB   1  4
> C.D  2  5
> E.F  3  6
> NA  NA NA
>  > data.frame(x=1:3,y=4:6,row.names=c("AB","C/D","E.F"))[c(1,1,2,3),]
>      x y
> AB  1 4
> AB1 1 4
> C.D 2 5
> E.F 3 6
>  > data.frame(x=1:3,y=4:6,row.names=c("AB","C/D","E.F"))[c("AB","C/D","E.F"),]
>      x y
> AB  1 4
> C/D 2 5
> E.F 3 6
>  >
> data.frame(x=1:3,y=4:6,row.names=c("AB","C/D","E.F"))[c("AB","C/D","E.F","NA"),]
>       x  y
> AB   1  4
> C.D  2  5
> E.F  3  6
> NA  NA NA
>  >
> data.frame(x=1:3,y=4:6,row.names=c("AB","C/D","E.F"))[c("AB","C/D","E.F",NA),]
>       x  y
> AB   1  4
> C.D  2  5
> E.F  3  6
> NA  NA NA
>  > version
>           _
> platform i386-pc-mingw32
> arch     i386
> os       mingw32
> system   i386, mingw32
> status   Patched
> major    1
> minor    5.0
> year     2002
> month    05
> day      16
> language R
>
>
>
>
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-- 
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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