Trait itertools::Itertools [−] [src]

pub trait Itertools: Iterator {
    fn interleave<J>(self, other: J) -> Interleave<Self, J::IntoIter> where J: IntoIterator<Item=Self::Item>, Self: Sized { ... }
    fn interleave_shortest<J>(self,
                          other: J)
                          -> InterleaveShortest<Self, J::IntoIter> where J: IntoIterator<Item=Self::Item>, Self: Sized { ... }
    fn intersperse(self, element: Self::Item) -> Intersperse<Self> where Self: Sized, Self::Item: Clone { ... }
    fn zip_longest<J>(self, other: J) -> ZipLongest<Self, J::IntoIter> where J: IntoIterator, Self: Sized { ... }
    fn zip_eq<J>(self, other: J) -> ZipEq<Self, J::IntoIter> where J: IntoIterator, Self: Sized { ... }
    fn batching<B, F>(self, f: F) -> Batching<Self, F> where F: FnMut(&mut Self) -> Option<B>, Self: Sized { ... }
    fn group_by<K, F>(self, key: F) -> GroupBy<K, Self, F> where Self: Sized, F: FnMut(&Self::Item) -> K { ... }
    fn group_by_lazy<K, F>(self, key: F) -> GroupBy<K, Self, F> where Self: Sized, F: FnMut(&Self::Item) -> K { ... }
    fn chunks(self, size: usize) -> IntoChunks<Self> where Self: Sized { ... }
    fn chunks_lazy(self, size: usize) -> IntoChunks<Self> where Self: Sized { ... }
    fn tuple_windows<T>(self) -> TupleWindows<Self, T> where Self: Sized + Iterator<Item=T::Item>, T: TupleCollect, T::Item: Clone { ... }
    fn tuples<T>(self) -> Tuples<Self, T> where Self: Sized + Iterator<Item=T::Item>, T: TupleCollect { ... }
    fn tee(self) -> (Tee<Self>, Tee<Self>) where Self: Sized, Self::Item: Clone { ... }
    fn step(self, n: usize) -> Step<Self> where Self: Sized { ... }
    fn merge<J>(self, other: J) -> Merge<Self, J::IntoIter> where Self: Sized, Self::Item: PartialOrd, J: IntoIterator<Item=Self::Item> { ... }
    fn merge_by<J, F>(self, other: J, is_first: F) -> MergeBy<Self, J::IntoIter, F> where Self: Sized, J: IntoIterator<Item=Self::Item>, F: FnMut(&Self::Item, &Self::Item) -> bool { ... }
    fn kmerge(self) -> KMerge<Self::Item::IntoIter> where Self: Sized, Self::Item: IntoIterator, Self::Item::Item: Ord { ... }
    fn cartesian_product<J>(self, other: J) -> Product<Self, J::IntoIter> where Self: Sized, Self::Item: Clone, J: IntoIterator, J::IntoIter: Clone { ... }
    fn coalesce<F>(self, f: F) -> Coalesce<Self, F> where Self: Sized, F: FnMut(Self::Item, Self::Item) -> Result<Self::Item, (Self::Item, Self::Item)> { ... }
    fn dedup(self) -> Dedup<Self> where Self: Sized, Self::Item: PartialEq { ... }
    fn unique(self) -> Unique<Self> where Self: Sized, Self::Item: Clone + Eq + Hash { ... }
    fn unique_by<V, F>(self, f: F) -> UniqueBy<Self, V, F> where Self: Sized, V: Eq + Hash, F: FnMut(&Self::Item) -> V { ... }
    fn take_while_ref<'a, F>(&'a mut self, f: F) -> TakeWhileRef<'a, Self, F> where Self: Clone, F: FnMut(&Self::Item) -> bool { ... }
    fn while_some<A>(self) -> WhileSome<Self> where Self: Sized + Iterator<Item=Option<A>> { ... }
    fn tuple_combinations<T>(self) -> TupleCombinations<Self, T> where Self: Sized + Clone, Self::Item: Clone, T: HasCombination<Self> { ... }
    fn combinations(self, n: usize) -> Combinations<Self> where Self: Sized, Self::Item: Clone { ... }
    fn pad_using<F>(self, min: usize, f: F) -> PadUsing<Self, F> where Self: Sized, F: FnMut(usize) -> Self::Item { ... }
    fn flatten(self) -> Flatten<Self, Self::Item::IntoIter> where Self: Sized, Self::Item: IntoIterator { ... }
    fn next_tuple<T>(&mut self) -> Option<T> where Self: Sized + Iterator<Item=T::Item>, T: TupleCollect { ... }
    fn find_position<P>(&mut self, pred: P) -> Option<(usize, Self::Item)> where P: FnMut(&Self::Item) -> bool { ... }
    fn dropping(self, n: usize) -> Self where Self: Sized { ... }
    fn dropping_back(self, n: usize) -> Self where Self: Sized, Self: DoubleEndedIterator { ... }
    fn foreach<F>(&mut self, f: F) where F: FnMut(Self::Item) { ... }
    fn collect_vec(self) -> Vec<Self::Item> where Self: Sized { ... }
    fn set_from<'a, A: 'a, J>(&mut self, from: J) -> usize where Self: Iterator<Item=&'a mut A>, J: IntoIterator<Item=A> { ... }
    fn join(&mut self, sep: &str) -> String where Self::Item: Display { ... }
    fn format(self, sep: &str) -> Format<Self> where Self: Sized { ... }
    fn format_default(self, sep: &str) -> Format<Self> where Self: Sized { ... }
    fn format_with<F>(self, sep: &str, format: F) -> FormatWith<Self, F> where Self: Sized, F: FnMut(Self::Item, &mut FnMut(&Display) -> Result) -> Result { ... }
    fn fold_results<A, E, B, F>(&mut self, start: B, f: F) -> Result<B, E> where Self: Iterator<Item=Result<A, E>>, F: FnMut(B, A) -> B { ... }
    fn fold_options<A, B, F>(&mut self, start: B, f: F) -> Option<B> where Self: Iterator<Item=Option<A>>, F: FnMut(B, A) -> B { ... }
    fn fold1<F>(&mut self, f: F) -> Option<Self::Item> where F: FnMut(Self::Item, Self::Item) -> Self::Item { ... }
    fn fold_while<B, F>(self, init: B, f: F) -> B where Self: Sized, F: FnMut(B, Self::Item) -> FoldWhile<B> { ... }
    fn sorted(self) -> Vec<Self::Item> where Self: Sized, Self::Item: Ord { ... }
    fn sorted_by<F>(self, cmp: F) -> Vec<Self::Item> where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering { ... }
    fn partition_map<A, B, F, L, R>(self, predicate: F) -> (A, B) where Self: Sized, F: Fn(Self::Item) -> Either<L, R>, A: Default + Extend<L>, B: Default + Extend<R> { ... }
    fn minmax(self) -> MinMaxResult<Self::Item> where Self: Sized, Self::Item: Ord { ... }
    fn minmax_by_key<K, F>(self, key: F) -> MinMaxResult<Self::Item> where Self: Sized, K: Ord, F: FnMut(&Self::Item) -> K { ... }
    fn minmax_by<F>(self, compare: F) -> MinMaxResult<Self::Item> where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering { ... }
}

The trait Itertools: extra iterator adaptors and methods for iterators.

This trait defines a number of methods. They are divided into two groups:

  • Adaptors take an iterator and parameter as input, and return a new iterator value. These are listed first in the trait. An example of an adaptor is .interleave()

  • Regular methods are those that don't return iterators and instead return a regular value of some other kind. .next_tuple() is an example and the first regular method in the list.

Provided Methods

Alternate elements from two iterators until both run out.

Iterator element type is Self::Item.

This iterator is fused.

use itertools::Itertools;

let it = (0..3).interleave(vec![7, 8]);
itertools::assert_equal(it, vec![0, 7, 1, 8, 2]);

Alternate elements from two iterators until one of them runs out.

Iterator element type is Self::Item.

use itertools::Itertools;

let it = (0..5).interleave_shortest(vec![7, 8]);
itertools::assert_equal(it, vec![0, 7, 1, 8, 2]);

An iterator adaptor to insert a particular value between each element of the adapted iterator.

Iterator element type is Self::Item.

This iterator is fused.

use itertools::Itertools;

itertools::assert_equal((0..3).intersperse(8), vec![0, 8, 1, 8, 2]);

Create an iterator which iterates over both this and the specified iterator simultaneously, yielding pairs of two optional elements.

This iterator is fused.

When both iterators return None, all further invocations of .next() will return None.

Iterator element type is EitherOrBoth<Self::Item, J::Item>.

use itertools::EitherOrBoth::{Both, Right};
use itertools::Itertools;
let it = (0..1).zip_longest(1..3);
itertools::assert_equal(it, vec![Both(0, 1), Right(2)]);

Create an iterator which iterates over both this and the specified iterator simultaneously, yielding pairs of elements.

Panics if the iterators reach an end and they are not of equal lengths.

A “meta iterator adaptor”. Its closure recives a reference to the iterator and may pick off as many elements as it likes, to produce the next iterator element.

Iterator element type is B.

use itertools::Itertools;

// An adaptor that gathers elements up in pairs
let pit = (0..4).batching(|mut it| {
           match it.next() {
               None => None,
               Some(x) => match it.next() {
                   None => None,
                   Some(y) => Some((x, y)),
               }
           }
       });

itertools::assert_equal(pit, vec![(0, 1), (2, 3)]);

Return an iterable that can group iterator elements. Consecutive elements that map to the same key (“runs”), are assigned to the same group.

GroupBy is the storage for the lazy grouping operation.

If the groups are consumed in order, or if each group's iterator is dropped without keeping it around, then GroupBy uses no allocations. It needs allocations only if several group iterators are alive at the same time.

This type implements IntoIterator (it is not an iterator itself), because the group iterators need to borrow from this value. It should be stored in a local variable or temporary and iterated.

Iterator element type is (K, Group): the group's key and the group iterator.

use itertools::Itertools;

// group data into runs of larger than zero or not.
let data = vec![1, 3, -2, -2, 1, 0, 1, 2];
// groups:     |---->|------>|--------->|

// Note: The `&` is significant here, `GroupBy` is iterable
// only by reference. You can also call `.into_iter()` explicitly.
for (key, group) in &data.into_iter().group_by(|elt| *elt >= 0) {
    // Check that the sum of each group is +/- 4.
    assert_eq!(4, group.sum::<i32>().abs());
}

Deprecated

: renamed to .group_by()

Return an iterable that can chunk the iterator.

Yield subiterators (chunks) that each yield a fixed number elements, determined by size. The last chunk will be shorter if there aren't enough elements.

IntoChunks is based on GroupBy: it is iterable (implements IntoIterator, not Iterator), and it only buffers if several chunk iterators are alive at the same time.

Iterator element type is Chunk, each chunk's iterator.

Panics if size is 0.

use itertools::Itertools;

let data = vec![1, 1, 2, -2, 6, 0, 3, 1];
//chunk size=3 |------->|-------->|--->|

// Note: The `&` is significant here, `IntoChunks` is iterable
// only by reference. You can also call `.into_iter()` explicitly.
for chunk in &data.into_iter().chunks(3) {
    // Check that the sum of each chunk is 4.
    assert_eq!(4, chunk.sum());
}

Deprecated

: renamed to .chunks()

Return an iterator over all contiguous windows producing tuples of a specific size (up to 4).

tuple_windows clones the iterator elements so that they can be part of successive windows, this makes it most suited for iterators of references and other values that are cheap to copy.

use itertools::Itertools;
let mut v = Vec::new();
for (a, b) in (1..5).tuple_windows() {
    v.push((a, b));
}
assert_eq!(v, vec![(1, 2), (2, 3), (3, 4)]);

let mut it = (1..5).tuple_windows();
assert_eq!(Some((1, 2, 3)), it.next());
assert_eq!(Some((2, 3, 4)), it.next());
assert_eq!(None, it.next());

// this requires a type hint
let it = (1..5).tuple_windows::<(_, _, _)>();
itertools::assert_equal(it, vec![(1, 2, 3), (2, 3, 4)]);

// you can also specify the complete type
use itertools::TupleWindows;
use std::ops::Range;

let it: TupleWindows<Range<u32>, (u32, u32, u32)> = (1..5).tuple_windows();
itertools::assert_equal(it, vec![(1, 2, 3), (2, 3, 4)]);

Return an iterator that groups the items in tuples of a specific size (up to 4).

See also the method .next_tuple().

use itertools::Itertools;
let mut v = Vec::new();
for (a, b) in (1..5).tuples() {
    v.push((a, b));
}
assert_eq!(v, vec![(1, 2), (3, 4)]);

let mut it = (1..7).tuples();
assert_eq!(Some((1, 2, 3)), it.next());
assert_eq!(Some((4, 5, 6)), it.next());
assert_eq!(None, it.next());

// this requires a type hint
let it = (1..7).tuples::<(_, _, _)>();
itertools::assert_equal(it, vec![(1, 2, 3), (4, 5, 6)]);

// you can also specify the complete type
use itertools::Tuples;
use std::ops::Range;

let it: Tuples<Range<u32>, (u32, u32, u32)> = (1..7).tuples();
itertools::assert_equal(it, vec![(1, 2, 3), (4, 5, 6)]);

See also Tuples::into_buffer.

Split into an iterator pair that both yield all elements from the original iterator.

Note: If the iterator is clonable, prefer using that instead of using this method. It is likely to be more efficient.

Iterator element type is Self::Item.

use itertools::Itertools;
let xs = vec![0, 1, 2, 3];

let (mut t1, t2) = xs.into_iter().tee();
itertools::assert_equal(t1.next(), Some(0));
itertools::assert_equal(t2, 0..4);
itertools::assert_equal(t1, 1..4);

Return an iterator adaptor that steps n elements in the base iterator for each iteration.

The iterator steps by yielding the next element from the base iterator, then skipping forward n - 1 elements.

Iterator element type is Self::Item.

Panics if the step is 0.

use itertools::Itertools;

let it = (0..8).step(3);
itertools::assert_equal(it, vec![0, 3, 6]);

Return an iterator adaptor that merges the two base iterators in ascending order. If both base iterators are sorted (ascending), the result is sorted.

Iterator element type is Self::Item.

use itertools::Itertools;

let a = (0..11).step(3);
let b = (0..11).step(5);
let it = a.merge(b);
itertools::assert_equal(it, vec![0, 0, 3, 5, 6, 9, 10]);

Return an iterator adaptor that merges the two base iterators in order. This is much like .merge() but allows for a custom ordering.

This can be especially useful for sequences of tuples.

Iterator element type is Self::Item.

use itertools::Itertools;

let a = (0..).zip("bc".chars());
let b = (0..).zip("ad".chars());
let it = a.merge_by(b, |x, y| x.1 <= y.1);
itertools::assert_equal(it, vec![(0, 'a'), (0, 'b'), (1, 'c'), (1, 'd')]);

Return an iterator adaptor that flattens an iterator of iterators by merging them in ascending order.

If all base iterators are sorted (ascending), the result is sorted.

Iterator element type is Self::Item.

use itertools::Itertools;

let a = (0..6).step(3);
let b = (1..6).step(3);
let c = (2..6).step(3);
let it = vec![a, b, c].into_iter().kmerge();
itertools::assert_equal(it, vec![0, 1, 2, 3, 4, 5]);

Return an iterator adaptor that iterates over the cartesian product of the element sets of two iterators self and J.

Iterator element type is (Self::Item, J::Item).

use itertools::Itertools;

let it = (0..2).cartesian_product("αβ".chars());
itertools::assert_equal(it, vec![(0, 'α'), (0, 'β'), (1, 'α'), (1, 'β')]);

Return an iterator adaptor that uses the passed-in closure to optionally merge together consecutive elements.

The closure f is passed two elements, x, y and may return either (1) Ok(z) to merge the two values or (2) Err((x', y')) to indicate they can't be merged. In (2), the value x' is emitted by the iterator. Coalesce continues with either z (1) or y' (2), and the next iterator element as the next pair of elements to merge.

Iterator element type is Self::Item.

This iterator is fused.

use itertools::Itertools;

// sum same-sign runs together
let data = vec![-1., -2., -3., 3., 1., 0., -1.];
itertools::assert_equal(data.into_iter().coalesce(|x, y|
        if (x >= 0.) == (y >= 0.) {
            Ok(x + y)
        } else {
            Err((x, y))
        }),
        vec![-6., 4., -1.]);

Remove duplicates from sections of consecutive identical elements. If the iterator is sorted, all elements will be unique.

Iterator element type is Self::Item.

This iterator is fused.

use itertools::Itertools;

let data = vec![1., 1., 2., 3., 3., 2., 2.];
itertools::assert_equal(data.into_iter().dedup(),
                        vec![1., 2., 3., 2.]);

Return an iterator adaptor that filters out elements that have already been produced once during the iteration. Duplicates are detected using hash and equality.

Clones of visited elements are stored in a hash set in the iterator.

use itertools::Itertools;

let data = vec![10, 20, 30, 20, 40, 10, 50];
itertools::assert_equal(data.into_iter().unique(),
                        vec![10, 20, 30, 40, 50]);

Return an iterator adaptor that filters out elements that have already been produced once during the iteration.

Duplicates are detected by comparing the key they map to with the keying function f by hash and equality. The keys are stored in a hash set in the iterator.

use itertools::Itertools;

let data = vec!["a", "bb", "aa", "c", "ccc"];
itertools::assert_equal(data.into_iter().unique_by(|s| s.len()),
                        vec!["a", "bb", "ccc"]);

Return an iterator adaptor that borrows from a Clone-able iterator to only pick off elements while the predicate f returns true.

It uses the Clone trait to restore the original iterator so that the last and rejected element is still available when TakeWhileRef is done.

use itertools::Itertools;

let mut hexadecimals = "0123456789abcdef".chars();

let decimals = hexadecimals.take_while_ref(|c| c.is_numeric())
                           .collect::<String>();
assert_eq!(decimals, "0123456789");
assert_eq!(hexadecimals.next(), Some('a'));

Return an iterator adaptor that filters Option<A> iterator elements and produces A. Stops on the first None encountered.

Iterator element type is A, the unwrapped element.

use itertools::Itertools;

// List all hexadecimal digits
itertools::assert_equal(
    (0..).map(|i| std::char::from_digit(i, 16)).while_some(),
    "0123456789abcdef".chars());

Return an iterator adaptor that iterates over the combinations of the elements from an iterator.

Iterator element can be any homogeneous tuple of type Self::Item with size up to 4.

use itertools::Itertools;

let mut v = Vec::new();
for (a, b) in (1..5).tuple_combinations() {
    v.push((a, b));
}
assert_eq!(v, vec![(1, 2), (1, 3), (1, 4), (2, 3), (2, 4), (3, 4)]);

let mut it = (1..5).tuple_combinations();
assert_eq!(Some((1, 2, 3)), it.next());
assert_eq!(Some((1, 2, 4)), it.next());
assert_eq!(Some((1, 3, 4)), it.next());
assert_eq!(Some((2, 3, 4)), it.next());
assert_eq!(None, it.next());

// this requires a type hint
let it = (1..5).tuple_combinations::<(_, _, _)>();
itertools::assert_equal(it, vec![(1, 2, 3), (1, 2, 4), (1, 3, 4), (2, 3, 4)]);

// you can also specify the complete type
use itertools::TupleCombinations;
use std::ops::Range;

let it: TupleCombinations<Range<u32>, (u32, u32, u32)> = (1..5).tuple_combinations();
itertools::assert_equal(it, vec![(1, 2, 3), (1, 2, 4), (1, 3, 4), (2, 3, 4)]);

Return an iterator adaptor that iterates over the n-length combinations of the elements from an iterator.

Iterator element type is Vec<Self::Item>. The iterator produces a new Vec per iteration, and clones the iterator elements.

Panics if n is zero.

use itertools::Itertools;

let it = (1..5).combinations(3);
itertools::assert_equal(it, vec![
    vec![1, 2, 3],
    vec![1, 2, 4],
    vec![1, 3, 4],
    vec![2, 3, 4],
    ]);

Return an iterator adaptor that pads the sequence to a minimum length of min by filling missing elements using a closure f.

Iterator element type is Self::Item.

use itertools::Itertools;

let it = (0..5).pad_using(10, |i| 2*i);
itertools::assert_equal(it, vec![0, 1, 2, 3, 4, 10, 12, 14, 16, 18]);

let it = (0..10).pad_using(5, |i| 2*i);
itertools::assert_equal(it, vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);

let it = (0..5).pad_using(10, |i| 2*i).rev();
itertools::assert_equal(it, vec![18, 16, 14, 12, 10, 4, 3, 2, 1, 0]);

Unravel a nested iterator.

This is a shortcut for it.flat_map(|x| x).

use itertools::Itertools;

let data = vec![vec![1, 2, 3], vec![4, 5, 6]];
let flattened = data.into_iter().flatten();

itertools::assert_equal(flattened, vec![1, 2, 3, 4, 5, 6]);

Advances the iterator and returns the next items grouped in a tuple of a specific size (up to 4).

If there are enough elements to be grouped in a tuple, then the tuple is returned inside Some, otherwise None is returned.

use itertools::Itertools;

let mut iter = 1..5;

assert_eq!(Some((1, 2)), iter.next_tuple());

Find the position and value of the first element satisfying a predicate.

The iterator is not advanced past the first element found.

use itertools::Itertools;

let text = "Hα";
assert_eq!(text.chars().find_position(|ch| ch.is_lowercase()), Some((1, 'α')));

Consume the first n elements from the iterator eagerly, and return the same iterator again.

It works similarly to .skip( n ) except it is eager and preserves the iterator type.

use itertools::Itertools;

let mut iter = "αβγ".chars().dropping(2);
itertools::assert_equal(iter, "γ".chars());

Fusing notes: if the iterator is exhausted by dropping, the result of calling .next() again depends on the iterator implementation.

Consume the last n elements from the iterator eagerly, and return the same iterator again.

This is only possible on double ended iterators. n may be larger than the number of elements.

Note: This method is eager, dropping the back elements immediately and preserves the iterator type.

use itertools::Itertools;

let init = vec![0, 3, 6, 9].into_iter().dropping_back(1);
itertools::assert_equal(init, vec![0, 3, 6]);

Run the closure f eagerly on each element of the iterator.

Consumes the iterator until its end.

use std::sync::mpsc::channel;
use itertools::Itertools;

let (tx, rx) = channel();

// use .foreach() to apply a function to each value -- sending it
(0..5).map(|x| x * 2 + 1).foreach(|x| { tx.send(x).unwrap(); } );

drop(tx);

itertools::assert_equal(rx.iter(), vec![1, 3, 5, 7, 9]);

.collect_vec() is simply a type specialization of .collect(), for convenience.

Assign to each reference in self from the from iterator, stopping at the shortest of the two iterators.

The from iterator is queried for its next element before the self iterator, and if either is exhausted the method is done.

Return the number of elements written.

use itertools::Itertools;

let mut xs = [0; 4];
xs.iter_mut().set_from(1..);
assert_eq!(xs, [1, 2, 3, 4]);

Combine all iterator elements into one String, seperated by sep.

Use the Display implementation of each element.

use itertools::Itertools;

assert_eq!(["a", "b", "c"].iter().join(", "), "a, b, c");
assert_eq!([1, 2, 3].iter().join(", "), "1, 2, 3");

Format all iterator elements, separated by sep.

All elements are formatted (any formatting trait) with sep inserted between each element.

Panics if the formatter helper is formatted more than once.

use itertools::Itertools;

let data = [1.1, 2.71828, -3.];
assert_eq!(
    format!("{:.2}", data.iter().format(", ")),
           "1.10, 2.72, -3.00");

Deprecated

: renamed to .format()

Format all iterator elements, separated by sep.

This is a customizable version of .format().

The supplied closure format is called once per iterator element, with two arguments: the element and a callback that takes a &Display value, i.e. any reference to type that implements Display.

Using &format_args!(...) is the most versatile way to apply custom element formatting. The callback can be called multiple times if needed.

Panics if the formatter helper is formatted more than once.

use itertools::Itertools;

let data = [1.1, 2.71828, -3.];
let data_formatter = data.iter().format_with(", ", |elt, f| f(&format_args!("{:.2}", elt)));
assert_eq!(format!("{}", data_formatter),
           "1.10, 2.72, -3.00");

// .format_with() is recursively composable
let matrix = [[1., 2., 3.],
              [4., 5., 6.]];
let matrix_formatter = matrix.iter().format_with("\n", |row, f| {
                                f(&row.iter().format_with(", ", |elt, g| g(&elt)))
                             });
assert_eq!(format!("{}", matrix_formatter),
           "1, 2, 3\n4, 5, 6");

Fold Result values from an iterator.

Only Ok values are folded. If no error is encountered, the folded value is returned inside Ok. Otherwise, the operation terminates and returns the first Err value it encounters. No iterator elements are consumed after the first error.

The first accumulator value is the start parameter. Each iteration passes the accumulator value and the next value inside Ok to the fold function f and its return value becomes the new accumulator value.

For example the sequence Ok(1), Ok(2), Ok(3) will result in a computation like this:

let mut accum = start;
accum = f(accum, 1);
accum = f(accum, 2);
accum = f(accum, 3);

With a start value of 0 and an addition as folding function, this effetively results in ((0 + 1) + 2) + 3

use std::ops::Add;
use itertools::Itertools;

let values = [1, 2, -2, -1, 2, 1];
assert_eq!(
    values.iter()
          .map(Ok::<_, ()>)
          .fold_results(0, Add::add),
    Ok(3)
);
assert!(
    values.iter()
          .map(|&x| if x >= 0 { Ok(x) } else { Err("Negative number") })
          .fold_results(0, Add::add)
          .is_err()
);

Fold Option values from an iterator.

Only Some values are folded. If no None is encountered, the folded value is returned inside Some. Otherwise, the operation terminates and returns None. No iterator elements are consumed after the None.

This is the Option equivalent to fold_results.

use std::ops::Add;
use itertools::Itertools;

let mut values = vec![Some(1), Some(2), Some(-2)].into_iter();
assert_eq!(values.fold_options(5, Add::add), Some(5 + 1 + 2 - 2));

let mut more_values = vec![Some(2), None, Some(0)].into_iter();
assert!(more_values.fold_options(0, Add::add).is_none());
assert_eq!(more_values.next().unwrap(), Some(0));

Accumulator of the elements in the iterator.

Like .fold(), without a base case. If the iterator is empty, return None. With just one element, return it. Otherwise elements are accumulated in sequence using the closure f.

use itertools::Itertools;

assert_eq!((0..10).fold1(|x, y| x + y).unwrap_or(0), 45);
assert_eq!((0..0).fold1(|x, y| x * y), None);

An iterator method that applies a function, producing a single, final value.

fold_while() is basically equivalent to fold() but with additional support for early exit via short-circuiting.

use itertools::Itertools;
use itertools::FoldWhile::{Continue, Done};

let numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

let mut result = 0;

// for loop:
for i in &numbers {
    if *i > 5 {
        break;
    }
    result = result + i;
}

// fold:
let result2 = numbers.iter().fold(0, |acc, x| {
    if *x > 5 { acc } else { acc + x }
});

// fold_while:
let result3 = numbers.iter().fold_while(0, |acc, x| {
    if *x > 5 { Done(acc) } else { Continue(acc + x) }
});

// they're the same
assert_eq!(result, result2);
assert_eq!(result2, result3);

The big difference between the computations of result2 and result3 is that while fold() called the provided closure for every item of the callee iterator, fold_while() actually stopped iterating as soon as it encountered Fold::Done(_).

Collect all iterator elements into a sorted vector in ascending order.

Note: This consumes the entire iterator, uses the slice::sort_by() method and returns the sorted vector.

use itertools::Itertools;

// sort the letters of the text in ascending order
let text = "bdacfe";
itertools::assert_equal(text.chars().sorted(),
                        "abcdef".chars());

Collect all iterator elements into a sorted vector.

Note: This consumes the entire iterator, uses the slice::sort_by() method and returns the sorted vector.

use itertools::Itertools;

// sort people in descending order by age
let people = vec![("Jane", 20), ("John", 18), ("Jill", 30), ("Jack", 27)];

let oldest_people_first = people
    .into_iter()
    .sorted_by(|a, b| Ord::cmp(&b.1, &a.1))
    .into_iter()
    .map(|(person, _age)| person);

itertools::assert_equal(oldest_people_first,
                        vec!["Jill", "Jack", "Jane", "John"]);

Collect all iterator elements into one of two partitions. Unlike Iterator::partition, each partition may have a distinct type.

use itertools::{Itertools, Either};

let successes_and_failures = vec![Ok(1), Err(false), Err(true), Ok(2)];

let (successes, failures): (Vec<_>, Vec<_>) = successes_and_failures
    .into_iter()
    .partition_map(|r| {
        match r {
            Ok(v) => Either::Left(v),
            Err(v) => Either::Right(v),
        }
    });

assert_eq!(successes, [1, 2]);
assert_eq!(failures, [false, true]);

Return the minimum and maximum elements in the iterator.

The return type MinMaxResult is an enum of three variants:

  • NoElements if the iterator is empty.
  • OneElement(x) if the iterator has exactly one element.
  • MinMax(x, y) is returned otherwise, where x <= y. Two values are equal if and only if there is more than one element in the iterator and all elements are equal.

On an iterator of length n, min_max does 1.5 * n comparisons, and so is faster than calling min and max separately which does 2 * n comparisons.

Examples

use itertools::Itertools;
use itertools::MinMaxResult::{NoElements, OneElement, MinMax};

let a: [i32; 0] = [];
assert_eq!(a.iter().minmax(), NoElements);

let a = [1];
assert_eq!(a.iter().minmax(), OneElement(&1));

let a = [1, 2, 3, 4, 5];
assert_eq!(a.iter().minmax(), MinMax(&1, &5));

let a = [1, 1, 1, 1];
assert_eq!(a.iter().minmax(), MinMax(&1, &1));

Return the minimum and maximum element of an iterator, as determined by the specified function.

The return value is a variant of MinMaxResult like for minmax().

For the minimum, the first minimal element is returned. For the maximum, the last maximal element wins. This matches the behavior of the standard Iterator::min() and Iterator::max() methods.

Return the minimum and maximum element of an iterator, as determined by the specified comparison function.

The return value is a variant of MinMaxResult like for minmax().

For the minimum, the first minimal element is returned. For the maximum, the last maximal element wins. This matches the behavior of the standard Iterator::min() and Iterator::max() methods.

Implementors