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title: “Benchmarking Iteration”
output: rmarkdown::html_vignette
self_contained: yes
vignette: >

This document illustrates the differences in performance between iterors and previous packages iterators/itertools/itertools2. Basic gains come from the nextOr method avoiding the need for tryCatch, as well as the fact that iterors can be used simply as functions, skipping S3 dispatch. Additionally, over the process of curating the iterors package, several iterator implementations have been optimized for performance.

Because this is a more computationally intensive vignette, it is built manually and included in the released package statically. The Rmd source is in the Git repo under the scratch directory; knit it manually and copy it into the vignettes directory to publish. When this document was last built, it was under these conditions:

  • iterors version 1.0, git revision 257dc955 ()
  • itertools2 version 0.1.1
  • itertools version 0.1.3
  • OS: Linux 5.4.0-148-generic
  • CPU: Intel(R) Core(TM) i5 CPU M 520 @ 2.40GHz.
  • R version 4.3.0 (2023-04-21), svn rev 84292

Basic iterators (self-contained/memory-backed)

Consuming iterators

Since the following tests will use different versions of icount, iter_consume, and as.list, first check how close those functions are.

as.list.bench <- microbenchmark::microbenchmark(
  iter_consume = iter_consume(iterators::icount(3000)),
  iterors.consume = iterors::consume(iterors::icount(3000)),
  iterators.as_list = as.list(iterators::icount(3000)),
  iterors.as_list = as.list(iterors::icount(3000)),
  times = 10)

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Note that we are using our own function iter_consume, as itertools::consume has poor performance due to invoking try on every item.

Simple iteration over a vector

vector.bench <- microbenchmark::microbenchmark(
    iterators = iter_consume(iterators::iter(1:1000)),
    iterors = iterors::consume(iterors::iteror(1:1000)),
    times = 10)

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Chunking a vector

chunk.bench <- microbenchmark::microbenchmark(
  itertools = iter_consume(itertools::isplitVector(1:6000, chunkSize=17)),
  iterors = iterors::consume(iterors::iteror(1:6000, chunkSize=17)),
  times = 10)

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Extracting rows or columns

arr <- array(1:1000000, c(1000,1000))
slice.bench <- microbenchmark::microbenchmark(
  iterators.rows = iter_consume(iterators::iter(arr, by="row")),
  iterators.cols = iter_consume(iterators::iter(arr, by="column")),
  itertools.array_rows = iter_consume(itertools::iarray(arr, MARGIN = 1)),
  itertools.array_cols = iter_consume(itertools::iarray(arr,MARGIN = 2)),
  iterors.rows = iterors::consume(iterors::iteror(arr, by=1)),
  iterors.cols = iterors::consume(iterors::iteror(arr, by=2)),
times = 10)

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Split matrix into chunks

arr <- array(1:1000000, c(1000,1000))
array_chunks.bench <- microbenchmark::microbenchmark(
  itertools.rows = iter_consume(itertools::isplitRows(arr, chunkSize=7)),
  itertools.cols = iter_consume(itertools::isplitCols(arr, chunkSize=7)),
  iterors.rows = iterors::consume(iterors::iteror(arr, by=1, chunkSize=7)),
  iterors.cols = iterors::consume(iterors::iteror(arr, by=2, chunkSize=7)),
times = 10)

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Enumerating N-D array indices:

 icountn.bench <- microbenchmark::microbenchmark(
   iterators = iter_consume(iterators::icountn(c(4,5,6,7))),
    iterors = iterors::consume(iterors::icountn(c(4,5,6,7))),
    times =10)

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Cartesian product of vectors

igrid.bench <- microbenchmark::microbenchmark(
  # itertools2 = iter_consume(itertools2::iproduct(1:10, letters,,
  itertools = iter_consume(itertools::product(1:10, letters,,
  itertools2 = iter_consume(itertools2::iproduct(1:10, letters,,
  iterors = iterors::consume(iterors::igrid(1:10, letters,,
  times = 10)

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Random number generation

When independent=TRUE there is a slight amount of extra work in saving and restoring the random number generator settings. The difference becomes smaller the larger “n” you pick.

sampling.bench <- microbenchmark::microbenchmark(
    iterators = iter_consume(iterators::irunif(100, count=100)),
    iterors.independent =  as.list(iterors::irunif(100, count=100, independent=TRUE)),
    iterors.dependent = as.list(iterors::irunif(100, count=100, independent=FALSE)),
    times = 100)

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What are the costs of speed here? here?


Higher order iterators / iterator functions

Chaining iterators end-to-end

chain.bench <- microbenchmark::microbenchmark(
  itertools = iter_consume(,
            lapply(1:50, iterators::icount))),
    itertools2 = iter_consume(,
              lapply(1:50, iterators::icount))),
  iterors =
    iterors::consume(, lapply(1:50, iterors::icount))),
  iterors.collapse =
    iterors::consume(iterors::i_concat(iterors::i_apply(1:50, iterors::icount))),

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Keeping or dropping items according to a criterion

i_keep.bench <- microbenchmark::microbenchmark(
    iterators = as.list(itertools::ifilter(\(x) floor(sqrt(x))^2 == x, iterators::icount(5000))),
    iterors = as.list(iterors::i_keep(iterors::icount(5000), \(x) floor(sqrt(x))^2 == x)),
    times = 10)

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Select only unique values

iterors::i_unique uses a hash table for better performance.

i_unique.bench <- microbenchmark::microbenchmark(
       iterators = {
         it <- itertools2::iunique(iterators::isample(1:100, 1))
         as.numeric(itertools2::take(it, 100))
       iterors = {
         it <- iterors::i_unique(iterors::isample(1:100, 1, independent=FALSE))
         iterors::take(it, 100, "numeric")

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Note that itertools2::icycle only works for self-contained vector-based iterators, while the other two use a general purpose buffer.

icycle.bench <- microbenchmark::microbenchmark(
  itertools2 = as.list(itertools2::icycle(iterators::icount(20), times = 20)),
  itertools = iter_consume(itertools::recycle(iterators::icount(20), times = 20)),
  iterors = iterors::consume(iterors::i_recycle(iterors::icount(20), times = 20)),
  times = 20)

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Note that itertools2::tee only works for vector-based iterators it knows how to clone, while iterors::i_tee uses a general purpose buffering mechanism.

i_tee.bench <- microbenchmark::microbenchmark(
        itertools2::itee(1:20, n=20)))
        iterors::i_tee(iterors::icount(20), n=20)))

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Sliding window iterators

iterors uses specialized routines for n=2 and n=3. For n=4 and above, a general purpose queue is used.

  if (exists("itripletwise", asNamespace("itertools2"), inherits=FALSE)) {
    iterors.w2={iterors::consume(iterors::i_window(1:200, 2))},
    iterors.w3={iterors::consume(iterors::i_window(1:200, 3))},
    iterors.w4={iterors::consume(iterors::i_window(1:200, 4))},
    iterors.w50={iterors::consume(iterors::i_window(1:200, 50))}))
i_window.bench <- microbenchmark::microbenchmark(list=marks, times=10)

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