[R-sig-Geo] numeric(0) ?????

[Ole F. Christensen]

Dear Massimiliano


How about

for (i in 1:20){
if(any(T$pluto==i)) T$pippo[T$pluto==i]
}

??

Depending on what you want to do with these subsets of the data.frame, 
you might want to consider using
``tapply'' or ``by'' [se the help-files for these functions] instead of 
the for loop.

For example :

tapply(T$pluto,T$pippo, sum)

Cheers

Ole


Massimiliano Cannata wrote:

>hello,
>I have a little problem with my script:
>
>I select a subset from a data frame
> 
>for (i in 1:20){
>T$pippo[T$pluto==i]
>}
>
>but sometime it is void because T$pluto==5 does not exists, the R answer is:
>
>T$pippo[T$pluto==5]
>  
>
>>numeric(0)
>>    
>>
>
>how to exclude this null subset? 
>and what is numeric(0), similar to NA?
>I try an if statement, but how to write if T$pippo[T$pluto==i] is numeric(0)???
>
>Thanks a lot.
>Maxi
>
>
>-------------
>Ing.  Massimiliano Cannata
>Istituto di Scienze della Terra - SUPSI
>C.P. 72 - CH-6952 Canobbio (Ticino, Switzerland)
>Tel +41 91 /935 12 25 - Fax +41 91 /935 12 09
>eMail: massimiliano.cannata at supsi.ch
>Internet: http://www.ist.supsi.ch
>
>
>	[[alternative HTML version deleted]]
>
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>  
>

-- 
Ole F. Christensen
Center for Bioinformatik
Datalogisk Institut
Aarhus Universitet
Ny Munkegade, Bygning 540
8000 Aarhus C
Denmark