[R] sum specific rows in a data frame

[Jeff Newmiler]

This is good news, although I have recently encountered what I consider excessive memory usage in the addition of key columns that don't affect the number of groups.  For example, grouping by Year and Month, if I add MonthBegin, a POSIXct column from which the Year and Month columns were derived, I run out of memory. 

hadley wickham <h.wickham at gmail.com> 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
>
>
>-- 
>Assistant Professor / Dobelman Family Junior Chair
>Department of Statistics / Rice University
>http://had.co.nz/
>
>______________________________________________
>R-help at 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.