[R] case conversion and/or string comparison

David Barron david.barron at jesus.ox.ac.uk
Fri Nov 16 12:56:48 CET 2001

>  > grep("HGT", "hgt", ignore.case = T) == 1
>  [1] TRUE
>  > grep("HGT", "tem", ignore.case = T) == 1
>  logical(0)
> Note that the bottom is not 'FALSE'?  Why?

That's because grep returns the *indices* of the elements of x that yielded
a match.  If there are no matches, then grep returns a (numeric) vector of
length 0.  A quick and dirty way of achieving what you want would therefore
be to test the length of the vector returned, eg,

if (length(grep("HGT","tem",ignore.case=T))==0) print("hi")

I'm sure there is a better way, though!


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