Feature gate: #![feature(slice_group_by)]

This is a tracking issue for the GroupBy and GroupByMut iterators.

This feature exposes the group_by and group_by_mut methods on the slice and mutable slice types, these methods return the GroupBy and GroupByMut iterators structs respectively. Those two iterators return subslices of the original slice where a user-defined function returns true for two following elements of the slice.

Public API

These methods can return subslices that contains equal elements:

let slice = &[1, 1, 1, 3, 3, 2, 2, 2];

let mut iter = slice.group_by(|a, b| a == b);

assert_eq!(iter.next(), Some(&[1, 1, 1][..]));
assert_eq!(iter.next(), Some(&[3, 3][..]));
assert_eq!(iter.next(), Some(&[2, 2, 2][..]));
assert_eq!(iter.next(), None);

they can also be used to extract the sorted subslices:

let slice = &[1, 1, 2, 3, 2, 3, 2, 3, 4];

let mut iter = slice.group_by(|a, b| a <= b);

assert_eq!(iter.next(), Some(&[1, 1, 2, 3][..]));
assert_eq!(iter.next(), Some(&[2, 3][..]));
assert_eq!(iter.next(), Some(&[2, 3, 4][..]));
assert_eq!(iter.next(), None);

Steps / History

• Initial RFC discussion: RFC: Add the group_by and group_by_mut methods to slice rfcs#2477 (it was determined that an RFC wasn't needed)
• Implementation: The return of the GroupBy and GroupByMut iterators on slice #79895
• Stabilization PR

Unresolved Questions

• Should this be group_by? Or should we reserve that name for another higher-level combinator?
  RFC: Add the group_by and group_by_mut methods to slice rfcs#2477 (comment)