From thomas@biostat.washington.edu  Thu Dec 23 18:44:45 1999
From: thomas@biostat.washington.edu (Thomas Lumley)
Date: Thu, 23 Dec 1999 18:44:45 +0000 (GMT)
Subject: data.frame(I(matrix)) ? (PR#388)
In-Reply-To: <199912231817.TAA21718@pubhealth.ku.dk>
Message-ID: <Pine.LNX.4.10.9912231839020.12924-100000@gimel.biostat.washington.edu>

On Thu, 23 Dec 1999 jens.oehlschlaegel-akiyoshi@mdfactory.de wrote:

> 
> 
> I observe dificulties with using data.frame(I(matrix))
> 
> > mat <- matrix(letters, 2, 2)
> > dimnames(mat) <- list(c(1:2), c("x","y"))
> > mat
>   x   y
> 1 "a" "c"
> 2 "b" "d"
> 
> > dd <- data.frame(I(mat))
> > ddd
>   I.mat..x I.mat..y
> 1        a        a
> 2        b        b
> 3        c        c
> 
> doesn't look too bad,
> but,
> has only one column name:
> 
> > dimnames(dd)
> [[1]]
> [1] "1" "2"
> 
> [[2]]
> [1] "I.mat."
> 
> and unexpected structure
> > str(ddd)
> `data.frame':     3 obs. of  1 variable:
>  $ I.mat.: chr [1:3, 1:2] "a" "b" "c" "a" "b" "c"
>   ..- attr(*, "dimnames")=List of 2
>   .. ..$ : NULL
>   .. ..$ : chr  "x" "y"
>   ..- attr(*, "class")= chr "AsIs"
> >
> 
> column 1 is a matrix
> > ddd[,1]
>      x   y
> [1,] "a" "a"
> [2,] "b" "b"
> [3,] "c" "c"
> attr(,"class")
> [1] "AsIs"
> 
> This dataframe is not a simple list with each element representing one
> column.
> 
> Consequently, e.g.
> 
> > sapply(ddd, FUN=function(x)x)
>      I.mat.
> [1,] "a"
> [2,] "b"
> [3,] "c"
> [4,] "a"
> [5,] "b"
> [6,] "c"
> 

This is the Right Thing:  we use the fact that multicolumn things can be a
single column of a data frame in logistic regression and extensively in
the survival analysis functions (and probably other places).  However, it
does make it hard to turn a character matrix into a data frame.  Perhaps
there should be an option of some sort?

	-thomas




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data.frame(I(matrix)) ? (PR#388)
Thomas Lumley