[R] Vector docs

David Winsemius dwinsemius at comcast.net
Sun May 30 14:09:31 CEST 2010

On May 30, 2010, at 1:43 AM, info at whywouldwe.com wrote:

> Hi
> The docs for R are very practical, which is quite refreshing  
> compared to other languages, however I can't find any details about  
> all the things I can do with a vector. I'm expecting methods like  
> vector.contains('foo') and vector.remove('foo'), maybe those methods  
> don't exist but I'd love to find a page that details the ones that do.

Since vectors may contain named elements, your request is ambiguous. I  
cannot tell whether "foo" is a name or a value. It's also ambiguous  
because it's not clear what vector.contains() is supposed to return.  
If you read the introductory material, you should find that the  
function "[" is fairly fundamental to R operations.


 > x <- c(foo=3,bar=4)
 > x
foo bar
   3   4
 > x["foo"]
 > x[-"foo"]
Error in -"foo" : invalid argument to unary operator
# the negation operation on indices only works with numeric arguments
# grep and which provide numeric resutls that can be used for "removal".
 > x[grep("foo", names(x))]
 > x[-grep("foo", names(x))]
 > x[which(names(x)=="foo")]

Minus operations on numeric indices perform removal, at least to the  
extent of what is returned, but indexing does not do destructive  
removal unless accompanied by "<-" . In fact "[<-" is a function in  
its own right.

> I'd also like to find some docs about foreach loops (unless there's  
> a better way to iterate through a vector), I've only found mailing  
> list posts.

Indexed solution are preferred, so see above, but if you want to find  
the help page for the "for" function



David Winsemius, MD
West Hartford, CT

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