Crate itertools

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Extra iterator adaptors, functions and macros.

To extend Iterator with methods in this crate, import the Itertools trait:

use itertools::Itertools;

Now, new methods like interleave are available on all iterators:

use itertools::Itertools;

let it = (1..3).interleave(vec![-1, -2]);
itertools::assert_equal(it, vec![1, -1, 2, -2]);

Most iterator methods are also provided as functions (with the benefit that they convert parameters using IntoIterator):

use itertools::interleave;

for elt in interleave(&[1, 2, 3], &[2, 3, 4]) {
    /* loop body */

Crate Features

  • use_std
    • Enabled by default.
    • Disable to compile itertools using #![no_std]. This disables any items that depend on collections (like group_by, unique, kmerge, join and many more).

Rust Version

This version of itertools requires Rust 1.32 or later.



  • The concrete iterator types.
  • Traits helpful for using certain Itertools methods in generic contexts.


  • Chain zero or more iterators together into one sequence.
  • Create an iterator over the “cartesian product” of iterators.
  • Create an iterator running multiple iterators in lockstep.


  • A type returned by the diff_with function.
  • The enum Either with variants Left and Right is a general purpose sum type with two cases.
  • Value that either holds a single A or B, or both.
  • An enum used for controlling the execution of fold_while.
  • MinMaxResult is an enum returned by minmax.
  • The first component of the value yielded by WithPosition. Indicates the position of this element in the iterator results.


  • An Iterator blanket implementation that provides extra adaptors and methods.
  • An iterator that can be unzipped into multiple collections.
  • An iterator that allows peeking at an element before deciding to accept it.


  • Test whether the predicate holds for all elements in the iterable.
  • Test whether the predicate holds for any elements in the iterable.
  • Assert that two iterables produce equal sequences, with the same semantics as equal(a, b).
  • Takes two iterables and creates a new iterator over both in sequence.
  • Create an iterator that clones each element from &T to T
  • Combine all an iterator’s elements into one element by using Extend.
  • Create an iterator that maps for example iterators of ((A, B), C) to (A, B, C).
  • Compares every element yielded by both i and j with the given function in lock-step and returns a Diff which describes how j differs from i.
  • Iterate iterable with a running index.
  • Return true if both iterables produce equal sequences (elements pairwise equal and sequences of the same length), false otherwise.
  • Perform a fold operation over the iterable.
  • Create an iterator that interleaves elements in i and j.
  • Iterate iterable with a particular value inserted between each element.
  • Iterate iterable with a particular value created by a function inserted between each element.
  • Creates a new iterator that infinitely applies function to value and yields results.
  • Combine all iterator elements into one String, separated by sep.
  • Create an iterator that merges elements of the contained iterators using the ordering function.
  • Create an iterator that merges elements of the contained iterators.
  • Return the maximum value of the iterable.
  • Create an iterator that merges elements in i and j.
  • Return an iterator adaptor that merge-joins items from the two base iterators in ascending order.
  • Return the minimum value of the iterable.
  • An iterator adaptor that allows the user to peek at multiple .next() values without advancing the base iterator.
  • Converts an iterator of tuples into a tuple of containers.
  • An iterator that generalizes .zip() and allows running multiple iterators in lockstep.
  • Partition a sequence using predicate pred so that elements that map to true are placed before elements which map to false.
  • A drop-in replacement for std::iter::Peekable which adds a peek_nth method allowing the user to peek at a value several iterations forward without advancing the base iterator.
  • “Lift” a function of the values of an iterator so that it can process an iterator of Result values instead.
  • Create an iterator where you can put back a single item
  • Create an iterator where you can put back multiple values to the front of the iteration.
  • Return an iterator inside a Rc<RefCell<_>> wrapper.
  • repeat_callDeprecated
    An iterator source that produces elements indefinitely by calling a given closure.
  • Create an iterator that produces n repetitions of element.
  • Iterate iterable in reverse.
  • Sort all iterator elements into a new iterator in ascending order.
  • Creates a new unfold source with the specified closure as the “iterator function” and an initial state to eventually pass to the closure
  • zipDeprecated
    Converts the arguments to iterators and zips them.
  • Iterate i and j in lock step.