Question

I want to return a logical vector for regexp matches over a character vector, but match or %in do not seem to support regular expressions, e.g.:

> x <- c("Bill", "Brett", "Jane")
> grep("^B", x)
[1] 1 2
> x %in% "^B"
[1] FALSE FALSE FALSE

I would like this to return

[1] TRUE TRUE FALSE

Ideas?

Thanks,

Roberto

Answer 1

Just chain it:

> seq(along=(x)) %in% grep("^B", x)
[1]  TRUE  TRUE  FALSE

So you could write yourself a little helper function that does both as shown here. But I presume one of the grep() variants does that as well… Ah, yes, grepl() is your friend:

> grepl("^B", x)
[1]  TRUE  TRUE  FALSE

Nothing that a quick help(grep) can’t cure 😉