From: Roger D. Peng (firstname.lastname@example.org)
Date: Sun 09 May 2004 - 02:23:18 EST
You can access a column of a dataframe using $ but not a matrix.
That's just how it is. You can access a column of a matrix
via its column name using, for example
> m <- matrix(1:12, 4, 3)
> colnames(m) <- c("a", "b", "c")
> m[, "b"]
 5 6 7 8
> I'm using 1.9.0 on Windoze 2k and I created a numeric matrix and used
> colnames() to give it some column names, but if I try to select a
> column using matrixname$validname I get a null return but if I use
> matrixname[,4] it works fine. Looking at the help I think this is
> because a matrix is not a recursive structure and I think it's saying
> I shouldn't be surprised nor attempt this.
> I'm in the process of transferring all my stats work to R having used
> a mixture of SPSS, S and SAS (and snippets of other things) over the
> years so sorry if I'm being dumb but this surprised me and I'd love a
> kindly explanation as I thought indexing a matrix in this way was
> something I did regularly (I think the last time was actually using it
> on a dataframe though) and I also think it would be useful and produce
> more readable code if I could.
> Can some kindly soul explain?
> Remail@example.com mailing list
> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
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