[Rd] man page for as.matrix for data frames outdated?

Martin Maechler maechler at stat.math.ethz.ch
Fri Nov 3 09:26:17 CET 2006

>>>>> "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]
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


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