[R] building a data.frame from a matrix: preventing conversion to factors

Christian Gold c.gold at magnet.at
Wed Nov 14 07:22:23 CET 2007

Thanks for your reply. I have tried the reproducible example you have 
provided (thanks!) in 3 different versions of R, and get what you get in 
R version 2.5.1, but in 2.3.1 (which I normally use) and 2.1.0 (which I 
still have installed) I get factors.
I guess this means I should switch to the new version?


Prof Brian Ripley wrote:
> I am trying to build a data.frame from some vectors and some matrices
> and seem to be unable to find out how to do this without converting
> everything to factors.
> I can prevent conversion of the vectors by using I(), as explained in
> help(data.frame). However, this doesn't help with the matrices: if I try
> I() with the matrix, the matrix gets incorporated into the data frame as
> a whole, rather than as a list of vectors as it should be. ("as.is=T"
> doesn't help either, and neither does "options(stringsAsFactors = FALSE)".)
> I think we need the reproducible example we asked for.  I get
>> z <- matrix(letters[1:12], 4, 3)
>> z2 <- data.frame(x=1:4, z=z, stringsAsFactors=FALSE)
>> sapply(z2, class)
>           x         z.1         z.2         z.3
>   "integer" "character" "character" "character"
> so it is working as documented.  (BTW, using I() on a matrix is intended 
> to insert a matrix as a single entity, and as.is is not an argument to 
> data.frame.)

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