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