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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