One option is use this:

aggregate(list(t=tt$t), list(idx=tt$idx), length)

On Thu, Aug 28, 2008 at 4:36 PM, <Seeliger.Curt@epamail.epa.gov> wrote:

> Folks,
>
> I've been running into an odd situation that occurs when I use length()
> function with aggregate(), but not with either one separately.  Together,
> the results looks correct but is given an unexpected name. 'if
> (stringsAsFactors) factor(x) else x' instead of just 'x'.
>
> # Numbers work ok
> tt <- data.frame(idx=c(1,1,1,1,1,1,2,2,2,2,2,2)
>                ,n=c(1,3,5,7,5,5,2,4,8,16,4,4)
>                ,t=c(1,3,5,7,5,5,2,4,8,16,4,4)
>                ,stringsAsFactors=FALSE)
>
> aggregate(tt$t, list('idx'=tt$idx), length)
> aggregate(as.factor(tt$t), list('idx'=tt$idx), length)
>
> # Character data doesn't work right unless I convert the data to factors.
> tt <- data.frame(idx=c(1,1,1,1,1,1,2,2,2,2,2,2)
>                ,n=c('1','3','5','7','5','5','2','4','8','16','4','4')
>                ,t=c('1','3','5','7','5','5','2','4','8','16','4','4')
>                ,stringsAsFactors=FALSE)
>
> aggregate(tt$t, list('idx'=tt$idx), length)
> aggregate(as.factor(tt$t), list('idx'=tt$idx), length)
>
>
> Any idea what is going on here?  For the record, this also happens with
> the modalvalue() function defined at
> http://wiki.r-project.org/rwiki/doku.php?id=tips:stats-basic:modalvalue
> (which also relies on length() ).
>
> As a side note, this began as an attempt to determine sample size, for
> which I've defined a function count <- function(x) { length(na.omit(x)) }.
>  No doubt there's a built in function to do just that, but as a newbie
> I've yet to find it.
>
> Thank you for your help,
> cur
> --
> Curt Seeliger, Data Ranger
> Raytheon Information Services - Contractor to ORD
> seeliger.curt@epa.gov
> 541/754-4638
>
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>
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>



-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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