The which() function help page states that, in the default case, what the
function returns is:
" Basically, the result is (1:length(x))[x]."
That would only be true if there are not any NA values in x. I think it would
be more accurate to say:
"Basically, the result is (1:length(x))[!is.na(x) & x]."
The "strange" (IMHO) behavior of logical indexing in R makes it necessary to
exclude NA values.
For this reason, I use to wrap logical indices with which(). I would have
written the above expression as:
(1:length(x))[which(x)]
But that would have been a really bad explanation of how the which() function
works ;)
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