[R] sum specific rows in a data frame

[Matthew Dowle]

Or try data.table 1.4 on r-forge, its grouping is faster than aggregate :

         agg datatable
X10    0.012     0.008
X100   0.020     0.008
X1000  0.172     0.020
X10000 1.164     0.144
X1e.05 9.397     1.180

install.packages("data.table", repos="http://R-Forge.R-project.org")
require(data.table)
dt = as.data.table(df)
t3 <- system.time(zz3 <- dt[, list(sumflt=sum(fltval), sumint=sum
(intval)), by=id])

Matthew


On Thu, 15 Apr 2010 13:09:17 +0000, hadley wickham wrote:
> On Thu, Apr 15, 2010 at 1:16 AM, Chuck <vijay.nori at gmail.com> wrote:
>> Depending on the size of the dataframe and the operations you are
>> trying to perform, aggregate or ddply may be better.  In the function
>> below, df has the same structure as your dataframe.
> 
> Current version of plyr:
> 
>          agg  ddply
> X10    0.005  0.007
> X100   0.007  0.026
> X1000  0.086  0.248
> X10000 0.577  3.136
> X1e.05 4.493 44.147
> 
> Development version of plyr:
> 
>          agg ddply
> X10    0.003 0.005
> X100   0.007 0.007
> X1000  0.042 0.044
> X10000 0.410 0.443
> X1e.05 4.479 4.237
> 
> So there are some big speed improvements in the works.
> 
> Hadley