Message-ID: <AANLkTik=x--byRYYCAkRz9xZXa=rM5e7ttkY_yPYjAJF@mail.gmail.com>
Date: 2011-01-17T23:10:10Z
From: Hadley Wickham
Subject: Summing data frame columns on identical data
In-Reply-To: <AANLkTikepqoLsCdeR9wkkc3bgcr0JwM_dZqmyJrcz=N3@mail.gmail.com>
> library(plyr)
> # Function to sum y by A-B combinations for a generic data frame
> dsum <- function(d) ddply(d, .(A, B), summarise, sumY = sum(y))
See count in plyr 1.4 for a much much faster way of doing this.
Hadley
--
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/