[R] pattern matching

[Marc Schwartz]

on 10/26/2008 10:54 AM John Lande wrote:
> dear all,
> 
> I have a little problem I am doing a loop, witha grep function. sometimes it
> happens that  have the following results
> 
>> tmp <- grep("x", y)
>> tmp
> integer(0)
> 
> 
> how can I recognise this outcome? is.na is not working of course, so what
> else?
> 
> thank you

A typical approach is to use any():


y <- c(letters[1:3])

> y
[1] "a" "b" "c"

> any(grep("x", y))
[1] FALSE

> any(grep("c", y))
[1] TRUE

which returns a boolean that you can then test for and proceed accordingly.


HTH,

Marc Schwartz