EVOLUTION-MANAGER

Edit File: bigmean2.R

library(foreach) # Define a combine function for the partial results comb <- function(...) { n <- foreach(a=list(...), .combine='+') %do% a$n means <- foreach(a=list(...), .combine='+') %do% ((a$n / n) * a$means) list(n=n, means=means) } # initialize some parameters datafile <- 'germandata.txt' nrows <- 100 # germandata.txt only has 1000 rows of data # create an iterator over the data in the file it <- iread.table(datafile, nrows=nrows, header=FALSE, row.names=NULL) # Compute the mean of each of those fields, nrows records at a time print(system.time( r <- foreach(d=it, .combine=comb, .multicombine=TRUE, .final=function(a) a$mean) %do% list(n=nrow(d), means=mean(d)) )) print(r) # This is faster for small problems (when it may not matter), # but becomes slower (or fails) for big problems print(system.time({ d <- read.table(datafile) r <- mean(d) })) print(r)