[R] as.matrix does not turn data frame into character matrix

[Prof Brian Ripley]

At least in R 1.8.0 it is a list matrix:

> class(jank)
[1] "matrix"
> typeof(jank)
[1] "list"

The help page is not quite correct, as it does not mention what happens 
when you create a data frame with a *list* as a column.

How did you create this data frame?  Columns cortrange and logcortrange
are surely intended to be numeric columns, and it is pretty moot point if
it is a valid data frame (it should not be possible to create it with
data.frame, for example, and do.call("data.frame", unclass(junk)) fails).

Please note that R 1.8.0 is current: we are nowhere near` 7.0 or `7.0'.
A lot of error-checking/correction in the data.frame area was added in 
1.8.0.


On Thu, 16 Oct 2003, Jacob Wegelin wrote:

> 
> The as.matrix function behaves in a puzzling manner.  The help file says:
> "`as.matrix' is a generic function. The method for data frames will
>      convert any non-numeric column into a character vector using
>      `format' and so return a character matrix."
> But this does not appear to be the case in the following example. Instead,
> as.matrix turns a data.frame into a list, not a character matrix, which
> wreaks havoc with my old code.
> 
> junk<-
> structure(list(SUBNUM = structure(c(3, 4, 5, 7, 6), class = "factor",
> .Label = c("01",
> "02", "03", "04", "07", "08", "09", "10", "11", "12", "13", "16",
> "17", "18", "21", "22", "23", "24", "25", "26", "27", "28")),
>     AGE = c(7, 7, 10, 8, 5), DIAGNOSI = c(1, 1, 1, 1, 1), cortrange =
> structure(list(
>         "03" = 19.0674, "04" = 40.3009, "07" = 37.0205, "09" = 8.84131,
>         "08" = 10.9855), .Names = c("03", "04", "07", "09", "08"
>     )), logcortrange = structure(list("03" = 1.90097866386896,
>         "04" = 2.75040785570225, "07" = 3.15633470025647, "09" =
> 2.56744094585387,
>         "08" = 2.84160608522206), .Names = c("03", "04", "07",
>     "09", "08"))), .Names = c("SUBNUM", "AGE", "DIAGNOSI", "cortrange",
> "logcortrange"), row.names = c("03", "04", "07", "09", "08"), class =
> "data.frame")
> 
> > junk
>    SUBNUM AGE DIAGNOSI cortrange logcortrange
> 03     03   7        1   19.0674     1.900979
> 04     04   7        1   40.3009     2.750408
> 07     07  10        1   37.0205     3.156335
> 09     09   8        1   8.84131     2.567441
> 08     08   5        1   10.9855     2.841606
> 
> > jank<-as.matrix(junk)
> > jank
>    SUBNUM AGE DIAGNOSI cortrange logcortrange
> 03 "03"   7   1        19.0674   1.900979
> 04 "04"   7   1        40.3009   2.750408
> 07 "07"   10  1        37.0205   3.156335
> 09 "09"   8   1        8.84131   2.567441
> 08 "08"   5   1        10.9855   2.841606
> 
> Notice that the first column is character, whereas the other columns are plain numeric!
> This is *not* a matrix of character.
> 
> > dput(jank)
> structure(list("03", "04", "07", "09", "08", 7, 7, 10, 8, 5,
>     1, 1, 1, 1, 1, 19.0674, 40.3009, 37.0205, 8.84131, 10.9855,
>     1.90097866386896, 2.75040785570225, 3.15633470025647, 2.56744094585387,
>     2.84160608522206), .Dim = c(5, 5), .Dimnames = list(c("03",
> "04", "07", "09", "08"), c("SUBNUM", "AGE", "DIAGNOSI", "cortrange",
> "logcortrange")))
> 
> Is this a bug?
> 
> One result of this:
> 
> > cbind(dimnames(jank)[[1]], jank)
> Error in cbind(...) : cannot create a matrix from these types
> 
> (I'm using version 7.0, because the links for downloading version 7.1 are dead today:)
> 
> > version
>          _
> platform i386-pc-mingw32
> arch     i386
> os       mingw32
> system   i386, mingw32
> status
> major    1
> minor    7.0
> year     2003
> month    04
> day      16
> language R
> 
> Thanks for any information.
> 
> Jake
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> 
> 

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595