Re: [R] Summing data frame columns on identical data

2011-01-17 Thread Hadley Wickham
> 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 Statist

Re: [R] Summing data frame columns on identical data

2011-01-17 Thread Dennis Murphy
Hi: Try this based on the following toy example: ### Generate a list of named data frames # There are more efficient ways to do this with replicate, but I forgot :) # A function to generate a data frame dmake <- function() data.frame(A = factor(rep(1:5, each = 10)),

[R] Summing data frame columns on identical data

2011-01-17 Thread Steve Murray
Dear all, I have 9 data frames, and I'm simply trying to sum the values of column 3 (on a row-by-row basis). However, there are a slightly different number of rows in each data frame, so I'm receiving the following error: "Error in Ops.data.frame(mrunoff_207101[3], mrunoff_207102[3]) :   + on