A TC39 proposal to consume an iterator as either overlapping or non-overlapping subsequences of configurable size.
Stage: 2.7
Specification:https://tc39.es/proposal-iterator-chunking/
It can be useful to consume a stream by more than one value at a time. For example, certain algorithms require looking at adjacent elements.
This is commonly solved for non-overlapping subsequences with a "chunking" method that works like the following:
constdigits=()=>[0,1,2,3,4,5,6,7,8,9].values();letchunksOf2=Array.from(digits().chunks(2));// [ [0, 1], [2, 3], [4, 5], [6, 7], [8, 9] ]letchunksOf3=Array.from(digits().chunks(3));// [ [0, 1, 2], [3, 4, 5], [6, 7, 8], [9] ]letchunksOf4=Array.from(digits().chunks(4));// [ [0, 1, 2, 3], [4, 5, 6, 7], [8, 9] ]- pagination
- columnar/grid layouts, such as calendars
- batch/stream processing
- matrix operations
- formatting/encoding
- bucketing (using a computed chunk size, for iterators of known size)
When overlapping sequences are needed, this is commonly called a "sliding window".
letwindowsOf2=Array.from(digits().windows(2));// [ [0, 1], [1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 7], [7, 8], [8, 9] ]letwindowsOf3=Array.from(digits().windows(3));// [ [0, 1, 2], [1, 2, 3], [2, 3, 4], [3, 4, 5], [4, 5, 6], [5, 6, 7], [6, 7, 8], [7, 8, 9] ]letwindowsOf4=Array.from(digits().windows(4));// [ [0, 1, 2, 3], [1, 2, 3, 4], [2, 3, 4, 5], [3, 4, 5, 6], [4, 5, 6, 7], [5, 6, 7, 8], [6, 7, 8, 9] ]- running/continuous computations, such as averages
- context-sensitive algorithms, such as pairwise comparisons
- carousels and their analogues (when applied to an infinite cycle)
| language | library | chunks | windows | chunks of 0? | truncates windows? |
|---|---|---|---|---|---|
| C++ | std::ranges::views | chunk | slide | undefined behavior | no |
| Clojure | core | partition | partition | infinite empty lists | when insufficient padding; terminates after 1 |
| Elm | List.Extra | groupsOf | groupsOfWithStep | empty list | no |
| Haskell | split | chunksOf | divvy | infinite empty lists | yes |
| Java | Stream | Gatherers.windowFixed | Gatherers.windowSliding | throws | no, step not configurable |
| Kotlin | Iterable | chunked | windowed | throws | configurable via parameter |
| .NET | System.Linq | Enumerable.Chunk | -- | throws | N/A |
| PHP | array | array_chunk | -- | throws | N/A |
| Python | itertools (3.12) | batched | -- | ?? | N/A |
| Python | more-itertools | grouper | windowed | empty iterator | no, mandatory fill value |
| Ruby | Enumerable | each_slice | each_cons | throws | no, step not configurable |
| Rust | Iterator | array_chunks | map_windows | panics | no, step not configurable |
| Rust | slice | chunks | windows | panics | no, step not configurable |
| Scala | Seq | grouped | sliding | throws | yes |
| Swift | Sequence | -- | -- | N/A | N/A |
| library | chunks | windows | chunks of 0? | truncates windows? |
|---|---|---|---|---|
chunk | chunk | -- | coerces 0 to false 😞 | N/A |
extra-iterable | chunk | chunk | infinite empty arrays | yes |
iter-ops | page | -- | throws | N/A |
iter-tools | batch | window, windowAhead, windowBehind | throws | optionally |
iterablefu | chunk | -- | collects everything into a single array | N/A |
itertools-ts | chunkwise | chunkwiseOverlap | throws | yes |
| Lodash / Underscore | chunk | -- | infinite empty arrays | N/A |
| Ramda | splitEvery | aperture | infinite empty arrays | no |
| sequency | chunk | -- | throws | N/A |
| wu | chunk | -- | collects everything into a single array | N/A |
