The problem is this:
b <- factor(letters[1:3]) str(b[1])
Factor w/ 3 levels "a","b","c": 1
for (i in b) str(i)
int 1 int 2 int 3 So seems like the for loop had drop the factor attribute for `i'. This doesn't happen when one simply subset `b':
for (i in b) str(b[i])
Factor w/ 3 levels "a","b","c": 1 Factor w/ 3 levels "a","b","c": 2 Factor w/ 3 levels "a","b","c": 3 Andy
From: Samuelson, Frank* How does one loop over factors? Perhaps this is a newbie question. I tried:
b
[1] caseX caseY caseZ Levels: caseX caseY caseZ
length(b)
[1] 3
for (i in b) {
+ print (b == i) ; + print (i); + } [1] FALSE FALSE FALSE [1] 1 [1] FALSE FALSE FALSE [1] 2 [1] FALSE FALSE FALSE [1] 3
But that strangely doesn't work. I must protest the implications of the above. i , as an iterator, is supposed take on values from b, but never is it equivalent to any of the values in b. The above works correctly for numbers or arrays of character strings. What's up with factors? Thanks for any help. -Frank
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