Hi,
I vaguely remember this issue being discussed at some length in the
past, but am having trouble relocating the proper thread (defining an
adequate search string to do so):
---<---------------cut here---------------start-------------->---
R> foo <- data.frame(A=gl(2, 5, labels=letters[1:2]), X=runif(10))
R> foo$A[1] <- NA
R> foo$A == "b"
[1] NA FALSE FALSE FALSE FALSE TRUE TRUE TRUE TRUE TRUE
R> foo$A[foo$A == "b"]
[1] <NA> b b b b b
Levels: a b
R> foo$X[foo$A == "b"]
[1] NA 0.4425 0.7164 0.3171 0.1967 0.8300
R> foo[foo$A == "b", ]
A X
NA <NA> NA
6 b 0.4425
7 b 0.7164
8 b 0.3171
9 b 0.1967
10 b 0.8300
---<---------------cut here---------------end---------------->---
Why is foo$X[1] set to NA in that last call?
Cheers,
--
Seb
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