[R] function - access column

[David Winsemius]

On Oct 7, 2011, at 11:25 AM, Ana wrote:

> Thanks! It helps. I completely forgot about the colnames function
>
> I added a "which(colnames(m)==n)" to my own function and now I can
> access with no problem the column by the number instead of the name.
>

'which' returns a logical vector. You could have also used the grep  
expression with value=F (the default) since the '[ , ]' operation can  
also use numeric arguments. The fundamental error was in trying to use  
the "$" operator.

-- 
David.
>
>
> On Fri, Oct 7, 2011 at 5:09 PM, R. Michael Weylandt
> <michael.weylandt at gmail.com> <michael.weylandt at gmail.com> wrote:
>> Perhaps something like this:
>>
>> Test <- function(m){
>>     m <- if(is.character(m)) get(m) else m
>>     stopifnot(length(colnames(m))>0)
>>     n = colnames(m)
>>     # Process n however
>>     2* m[, n]
>> }
>>
>> That make sense?
>>
>> Hope it helps,
>> Michael
>>
>>
>> On Oct 7, 2011, at 11:03 AM, Ana <rrasterr at gmail.com> wrote:
>>
>>> How can I call matrix$col, inside a function?
>>> The matrix name is one of the variables of the function, while the
>>> column name I get by assuming that it should have a certain
>>> characters.
>>>
>>> something like this
>>>
>>> function(matrix){
>>> colname=as.name(grep("[A-T a-t]ting",colnames(matrix),value=TRUE))
>>> output=2*(matrix$colname)
>>> return(output)
>>> }
>>>
>>> The name of the column is Testing.
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT