itertools (version 0.1-3)

irecord: Record and replay iterators

Description

The irecord function records the values issued by a specified iterator to a file or connection object. The ireplay function returns an iterator that will replay those values. This is useful for iterating concurrently over multiple, large matrices or data frames that you can't keep in memory at the same time. These large objects can be recorded to files one at a time, and then be replayed concurrently using minimal memory.

Usage

irecord(con, iterable)
ireplay(con)

Arguments

con

A file path or open connection.

iterable

The iterable to record to the file.

Examples

suppressMessages(library(foreach))

m1 <- matrix(rnorm(70), 7, 10)
f1 <- tempfile()
irecord(f1, iter(m1, by='row', chunksize=3))

m2 <- matrix(1:50, 10, 5)
f2 <- tempfile()
irecord(f2, iter(m2, by='column', chunksize=3))

# Perform a simple out-of-core matrix multiply
p <- foreach(col=ireplay(f2), .combine='cbind') %:%
       foreach(row=ireplay(f1), .combine='rbind') %do% {
         row %*% col
       }

dimnames(p) <- NULL
print(p)
all.equal(p, m1 %*% m2)
unlink(c(f1, f2))