which LETTERS?

I'm confused:

Thanks in advance.

which(LETTERS == c("A"))

This computes

LETTERS == c("A")

then returns the indices where it is TRUE.  Since LETTERS has 26 
elements, but "A" has only one, the "A" is repeated 26 times.  Only the 
first one matches LETTERS.

[1] 1

which(LETTERS == c("A","B"))

The c("A", "B") needs to be repeated 13 times to get to length 26. Only 
the first two match.

[1] 1 2

which(LETTERS == c("A","B","C"))

c("A", "B", "C") can't be repeated a whole number of times to extend to 
length 26, so it is repeated 8 2/3 times, and you get a warning.

[1] 1 2 3
Warning message:
In LETTERS == c("A", "B", "C") :
   longer object length is not a multiple of shorter object length

You probably want to use

which(LETTERS %in% c("A","B","C"))

instead.

Duncan Murdoch

Charles Stangor
Professor
Dept of Psychology
University of Maryland
Academic Achievement Research Group <http://www.charlesstangor.com/AARG>

	[[alternative HTML version deleted]]

______________________________________________
R-help at 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.