R help - Oct 2008 - pattern matching

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

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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

On 26/10/2008 11:54 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?
length(integer(0)) is zero.  If you get any matches, you'll get a longer 
result.

Duncan Murdoch