R devel - Nov 2006 - man page for as.matrix for data frames outdated?

Hi again,


The man page for 'as.matrix' says:

     'as.matrix' is a generic function. The method for data frames will
     convert any non-numeric/complex column into a character vector
     using 'format' and so return a character matrix, except that
     all-logical data frames will be coerced to a logical matrix.

It's true that "all-logical data frames will be coerced to a logical
matrix":

    > fourLogicals <- 2:5>3
    > df1 <- data.frame(a=fourLogicals)
    > storage.mode(as.matrix(df1))
    [1] "logical"

Otherwise it's not true that 'as.matrix' will return a character
matrix:

    > fourInts <- 2:-1
    > df2 <- data.frame(a=fourLogicals, b=fourInts)
    > storage.mode(as.matrix(df2))
    [1] "integer"


    > fourDoubles <- rep(pi,4)
    > df3 <- data.frame(c=fourDoubles, a=fourLogicals, b=fourInts)
    > storage.mode(as.matrix(df3))
    [1] "double"


    > fourComplexes <- (-1:2)+3i
    > df4 <- data.frame(a=fourLogicals, d=fourComplexes, b=fourInts,
    c=fourDoubles)
    > storage.mode(as.matrix(df4))
    [1] "complex"

If one column is of mode character, then 'as.matrix' will effectively
return a character matrix:

    > df5 <- data.frame(toto=c("a","bb"),
titi=c(9,999))
    > storage.mode(as.matrix(df5))
    [1] "character"

Note that the doc says that "any non-numeric/complex column" will
be passed thru 'format' which seems to be exactly the other way
around:

    > as.matrix(df5)
      toto titi
    1 "a"  "  9"
    2 "bb" "999"

Anyway why one would like to have the numeric values passed
thru 'format' to start with?

This is in R-2.4.0 and recent R-devel.

Best,
H.

>>>>> "Herve" == Herve Pages <hpages at
fhcrc.org>
>>>>>     on Thu, 02 Nov 2006 20:46:01 -0800 writes:
    Herve> Hi again, The man page for 'as.matrix' says:

   >>      'as.matrix' is a generic function. The method
   >> for data frames will convert any non-numeric/complex
   >> column into a character vector using 'format' and so
   >> return a character matrix, except that all-logical
   >> data frames will be coerced to a logical matrix.

In very old versions of R (e.g. 0.3 from March 1996),

    is.numeric(<logical>)  was TRUE
and there the help page was entirely correct.

I think if you replace [in the above paragraph]
    "non-numeric/complex"
by  "non-(logical/numeric/complex)"

the help page is correct again.


    Herve> If one column is of mode character, then 'as.matrix'
    Herve> will effectively return a character matrix:

(as it says in the man page, and always did in all
 implementations of the S language)

    Herve> Note that the doc says that "any non-numeric/complex
    Herve> column" will be passed thru 'format' which seems to
    Herve> be exactly the other way around:

No!  You left off the second part of the statement cited initally.
Slightly reformulated:

	 Iff there's any non-(logical/numeric/complex) column,
	 that will have to be passed through format and hence
	 the result must be a character matrix 
	 and hence every other column also needs to be "formatted"


    >> as.matrix(df5)
    Herve>       toto titi 1 "a" " 9" 2 "bb"
"999"

    Herve> Anyway why one would like to have the numeric values
    Herve> passed thru 'format' to start with?

Recall: The result must be a matrix !
	If it can't be a numeric matrix the decision was it must
	be character.

BTW: Exactly because of your problems,  
     The function   data.matrix()  had been devised (long ago in
     pre-R times),
     and data.matrix  *is*  the first entry in "See Also" on the
     help page for as.matrix

Martin