[Rd] man page for as.matrix for data frames outdated?

From: Herve Pages <hpages_at_fhcrc.org>
Date: Fri 03 Nov 2006 - 04:46:01 GMT


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.



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