[R] "group by" functionality in R

[John Kane]

Two approaches
?aggregate or the reshape package

aggregate(xx$volume, list(day=xx$day), sum)

library(reshape)
names(xx)[3]  <- "value"
cast(xx, day ~ ., sum)


--- On Wed, 10/1/08, Max Rausch <maxrausch at gmail.com> wrote:

> From: Max Rausch <maxrausch at gmail.com>
> Subject: [R] "group by" functionality in R
> To: r-help at r-project.org
> Received: Wednesday, October 1, 2008, 9:58 AM
> I have a data frame with the following information
> 
>           day         hour    volume
> 1  2003-07-18   10      836700
> 2  2003-07-18   11      375000
> 3  2003-07-18   12      60000
> 4  2003-07-18    8       1020000
> 5  2003-07-18    9       390000
> 
> I have been trying create a new data frame with the
> following
> 
>           day  total_daily_volume
> 
> I can accomplish this by bringing the data to excel and
> using a pivot 
> table but I would like to be able to do in R. I have been
> searching for 
> several hours but I can not figure out how to  sum the  the
> volume of 
> each day.
> 
> Thanks,
> 
> Max
> 
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