[R] data frame component replacement: feature or bug?
mcw at ln.nimh.nih.gov
Sun Sep 5 23:08:28 CEST 1999
The following does not behave as I think it should, and as it seems to me
it has in the past (although I can't check this easily). I know it
happens in both R-0.64.2 and R-0.65.0 on an old Power Computing running
Linux-PPC 1999, and in R-0.64.2 on an SGI running Irix 6.5.
Try the following:
t1 <- data.frame(matrix(rnorm(16), nc=4))
X1 X2 X3 X4
1 -0.7206945 0.4511310 -1.0638681 -0.9128938
2 -1.6340557 -0.8063090 0.7753397 0.3607708
3 0.5999834 0.5256372 0.4393342 1.3218485
4 2.8542598 -2.8740136 2.0165816 -0.3026954
 4 4
> t1$X1 <- 1
> t1$X2 <- 2
Note that R accepts this. I think it's replaced t1$X1 with a
vector of 1's using the usual repeating rules, and similarly for
X2. So I should still have a 4 X 4 data frame.
R seems to think so too.
 4 4
Error: dim<- length of dims do not match the length of object
> t1[, 1:2]
whereas t1[,3:4] gives me a 4 x 2 data frame as I would expect.
It seems that the "listness" of t1 is beating out it's "matrixness"
(having dimension and so on). It is possible to get what I want with
t1$X1 <- rep(1, length(t1$X1)).
As I said before, I thought that t1$X1 <- 1 would replace the whole first
column of t1 with 1's. Did other people think so too? And is that in
fact the way R should work?
(This example used all numeric columns, in which case a matrix would work.
In some of my real applications, that's not necessarily practical.)
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