[R] field index given name.

[David Winsemius]

On Oct 12, 2009, at 3:22 AM, tdm wrote:

>
> Thanks - would never have guessed that. I eventually got the  
> following to do
> what I want...
>
>> colprob <- array(dim=NCOL(iris))
>> for(i in 1:NCOL(iris)){
> + colprob[i]=
> + ifelse(names(iris)[i] == 'Species',1,0.5)
> + }
>> colprob
> [1] 0.5 0.5 0.5 0.5 1.0
>
>

This would be more in keeping with the approah in R of avoiding loops  
when possble:

 > colprob <- array(dim=NCOL(iris))
 > colprob[] <- 0.5
 > colprob
[1] 0.5 0.5 0.5 0.5 0.5
 > colprob[names(iris) == "Species"] <- 1
 > colprob
[1] 0.5 0.5 0.5 0.5 1.0


-- 
David
>
>
> Schalk Heunis-2 wrote:
>>
>> Hi Phil
>> Try the following
>>> which(names(iris)=='Species')
>> [1] 5
>>
>> HTH
>> Schalk Heunis
>>
>> On Mon, Oct 12, 2009 at 8:53 AM, tdm <philb at philbrierley.com> wrote:
>>
>>>
>>> Hi,
>>>
>>> How do I access the index number of a field given I only know the  
>>> field
>>> name?
>>>
>>> eg - I want to set the probability of the field 'species' higher  
>>> than the
>>> other fields to use in sampling.
>>>
>>>> colprob <- array(dim=NCOL(iris))
>>>> for(i in 1:NCOL(iris)){colprob[i]=0.5}
>>>> colprob[iris$species] = 1 #this doesn't work
>>>> colprob
>>> [1] 0.5 0.5 0.5 0.5 0.5
>>>
>>>
>>>
>>>
>>>
>>> --
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>>>
>>> ______________________________________________
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>>>
>>
>> 	[[alternative HTML version deleted]]
>>
>> ______________________________________________
>> 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.
>>
>>
>
> -- 
> View this message in context: http://www.nabble.com/field-index-given-name.-tp25851216p25851466.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> 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
Heritage Laboratories
West Hartford, CT