Prof Brian D Ripley <ripley at stats.ox.ac.uk> writes:
> On Wed, 31 May 2000, Denis White wrote:
>
> > In Splus this works,
> >
> > > a <- data.frame(matrix(round(runif(10),0),nrow=2,ncol=5))
> > > a[a == 1] <- 2
> >
> > but in R only if a is matrix,
> >
> > > a[a == 1] <- 2
> > Error in [<-.data.frame(*tmp*, a == 1, value = 2) :
> > matrix subscripts not allowed in replacement
> >
> > Was this a design decision? Sorry if I missed it in
> > An Introduction to R.
>
> S-PLUS differs from the original S here, as I understand it.
> So it was an S-PLUS design decision as I understand it. S-PLUS says:
>
> else if(nargs() == 3) {
> # really ambiguous, but follow common use as if list,
> # except when one subscript is a logical matrix the shape of x, then treat
> # as if x were a matrix.
Semantically it is a rather strange thing to do since elements
in different columns of a data matrix can be of different type.
And some really weird stuff *does* happen in Splus 3.4:
> a<-data.frame(a=1:10,b=factor(1:10),c=I(as.character(1:10)))
> a[a==5]<-"x"
Warning messages:
replacement values not all in levels(x): NA''s generated
in:> "[<-.factor"(.A0,
i[, k, drop = T], value = .A1)> a
a b c
1 1 1 1
2 2 2 2
3 3 3 3
4 4 4 4
5 x NA x
6 6 6 6
7 7 7 7
8 8 8 8
9 9 9 9
10 10 10 10> a[a==4]<-"y"
Warning messages:
1: Data length is not an even multiple of group length
in:> split(Value,
factor(col(i)[i], levels = seq(len = ncol(i))))
2: replacement values not all in levels(x): NA''s generated
in:> "[<-.factor"(.\
A0, i[, k, drop = T], value = .A1)
3: replacement values not all in levels(x): NA''s generated
in:> "[<-.factor"(.\
A0, i[, k, drop = T], value = .A1)> a
a b c
1 1 1 1
2 2 2 2
3 3 3 3
4 NA NA 4
5 x NA x
6 6 6 6
7 7 7 7
8 8 8 8
9 9 9 9
10 10 10 10
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /''_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907
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