syrvn wrote:
Thanks again for your quick reply.
I understood your procedure but now it is even more strange why my
conversion does not work.
In your example, the NA values are in "brackets" <NA> and what your
procedure does is to
convert these <NA> values into NA and then it seems to be possible to use
data.matrix to
correctly convert the data.frame into a data.matrix. But the data I read
into R are already in that
form that the NA values are displayed as NA rather than <NA>. So the
conversion should actually work.
Have not followed this thread, but I think you're confused about what a
true NA value is, at least with factors. When values of a factor are
missing, they are printed <NA> to distinguish them from an actual factor
level of NA. Numeric missings are printed NA.
> f1 <- factor("NA")
> f1
[1] NA
Levels: NA
> is.na(f1)
[1] FALSE
vs.
> n1 <- c(NA)
> n1
[1] NA
> is.na(n1)
[1] TRUE
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