I think there might be a problem with this approach if roi, tid, rt,
and mood are the same for nonconsecutive rows.
--Gray
On Tue, Dec 8, 2009 at 9:29 AM, Nikhil Kaza <nikhil.l...@gmail.com> wrote:
> How about creating an index using multiple columns.
>
> a <- with(d, aggregate(dur, list(rt=rt,tid=tid,mood=mood,roi=roi), sum))
> b <- with(d, aggregate(x, list(rt=rt,tid=tid,mood=mood,roi=roi), mean))
> c <- merge(a, b, by=c("rt","tid","mood", "roi"))
>
> I suppose one could save some time by not running aggregate twice on the
> same dataset, but I am not sure how.
>
> Nikhil
>
> On 8 Dec 2009, at 7:50AM, Titus von der Malsburg wrote:
>
>> Hi, I have a data frame and want to merge adjacent rows if some condition
>> is
>> met. There's an obvious solution using a loop but it is prohibitively
>> slow
>> because my data frame is large. Is there an efficient canonical solution
>> for
>> that?
>>
>>> head(d)
>>
>> rt dur tid mood roi x
>> 55 5523 200 4 subj 9 5
>> 56 5523 52 4 subj 7 31
>> 57 5523 209 4 subj 4 9
>> 58 5523 188 4 subj 4 7
>> 70 4016 264 5 indic 9 51
>> 71 4016 195 5 indic 4 14
>>
>> The desired result would have consecutive rows with the same roi value
>> merged.
>> dur values should be added and x values averaged, other values don't
>> differ in
>> these rows and should stay the same.
>>
>>> head(result)
>>
>> rt dur tid mood roi x
>> 55 5523 200 4 subj 9 5
>> 56 5523 52 4 subj 7 31
>> 57 5523 397 4 subj 4 8
>> 70 4016 264 5 indic 9 51
>> 71 4016 195 5 indic 4 14
>>
>> There's also a solution using reshape. It uses an index for blocks
>>
>> d$index <- cumsum(c(TRUE,diff(d$roi)!=0))
>>
>> melts and then casts for every column using an appropriate fun.aggregate.
>> However, this is a bit cumbersome and also I'm not sure how to make sure
>> that
>> I get the original order of rows.
>>
>> Thanks for any suggestion.
>>
>> Titus
>>
>> ______________________________________________
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>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help@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.
>
--
Gray Calhoun
Assistant Professor of Economics
Iowa State University
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