The 'levels' is supposed to be the order in which you want the factors to be. You have specified levels=1:20 and there are no matching values in letters[1:20], therefore NAs:
> x <- factor(letters[1:20], levels=letters[20:1]) > x [1] a b c d e f g h i j k l m n o p q r s t Levels: t s r q p o n m l k j i h g f e d c b a > x <- factor(letters[1:20], levels=LETTERS[20:1]) # error no matching levels > x [1] <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> [20] <NA> Levels: T S R Q P O N M L K J I H G F E D C B A > x <- factor(letters[1:20]) > x [1] a b c d e f g h i j k l m n o p q r s t Levels: a b c d e f g h i j k l m n o p q r s t > as.integer(x) [1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 > You can see in the last statement that the integer values for x are numbered, probably as you were expecting them. On Sat, Aug 2, 2008 at 5:48 PM, <[EMAIL PROTECTED]> wrote: > Doing ?factor I get: > > x a vector of data, usually taking a small number of distinct values. > levels an optional vector of the values that x might have taken. The default > is the set of values taken by x, sorted into increasing order. > > So if I do: > > factor(letters[1:20],level=seq(1:20) > [1] <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> > <NA> > [16] <NA> <NA> <NA> <NA> <NA> > Levels: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 > > So why all of the NA? What happend to 'a'. 'b', etc.? I was expecting a=1, > b=2, c=3 etc. > > I am missing something. Please help with my understanding. > > Keviin > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- Jim Holtman Cincinnati, OH +1 513 646 9390 What is the problem that you are trying to solve? ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
