Adds .permutations(k) adaptor

Author: tobz1000

benches/bench1.rs

@@ -7,10 +7,11 @@ use test::{black_box};
 use itertools::Itertools;
 
 use itertools::free::cloned;
+use itertools::Permutations;
 
 use std::iter::repeat;
 use std::cmp;
-use std::ops::Add;
+use std::ops::{Add, Range};
 
 mod extra;
 
@@ -762,3 +763,44 @@ fn all_equal_default(b: &mut test::Bencher) {
 
     b.iter(|| xs.iter().dedup().nth(1).is_none())
 }
+
+const PERM_COUNT: usize = 6;
+
+#[bench]
+fn permutations_iter(b: &mut test::Bencher) {
+    struct NewIterator(Range<usize>);
+
+    impl Iterator for NewIterator {
+        type Item = usize;
+
+        fn next(&mut self) -> Option<Self::Item> {
+            self.0.next()
+        }
+    }
+
+    b.iter(|| {
+        for _ in NewIterator(0..PERM_COUNT).permutations(PERM_COUNT) {
+
+        }
+    })
+}
+
+#[bench]
+fn permutations_range(b: &mut test::Bencher) {
+    b.iter(|| {
+        for _ in (0..PERM_COUNT).permutations(PERM_COUNT) {
+
+        }
+    })
+}
+
+#[bench]
+fn permutations_slice(b: &mut test::Bencher) {
+    let v = (0..PERM_COUNT).collect_vec();
+
+    b.iter(|| {
+        for _ in v.as_slice().iter().permutations(PERM_COUNT) {
+
+        }
+    })
+}

src/combinations.rs

@@ -2,12 +2,12 @@ use std::fmt;
 
 use super::lazy_buffer::LazyBuffer;
 
-/// An iterator to iterate through all the `n`-length combinations in an iterator.
+/// An iterator to iterate through all the `k`-length combinations in an iterator.
 ///
 /// See [`.combinations()`](../trait.Itertools.html#method.combinations) for more information.
 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
 pub struct Combinations<I: Iterator> {
-    n: usize,
+    k: usize,
     indices: Vec<usize>,
     pool: LazyBuffer<I>,
     first: bool,
@@ -17,27 +17,27 @@ impl<I> fmt::Debug for Combinations<I>
     where I: Iterator + fmt::Debug,
           I::Item: fmt::Debug,
 {
-    debug_fmt_fields!(Combinations, n, indices, pool, first);
+    debug_fmt_fields!(Combinations, k, indices, pool, first);
 }
 
 /// Create a new `Combinations` from a clonable iterator.
-pub fn combinations<I>(iter: I, n: usize) -> Combinations<I>
+pub fn combinations<I>(iter: I, k: usize) -> Combinations<I>
     where I: Iterator
 {
-    let mut indices: Vec<usize> = Vec::with_capacity(n);
-    for i in 0..n {
+    let mut indices: Vec<usize> = Vec::with_capacity(k);
+    for i in 0..k {
         indices.push(i);
     }
     let mut pool: LazyBuffer<I> = LazyBuffer::new(iter);
 
-    for _ in 0..n {
+    for _ in 0..k {
         if !pool.get_next() {
             break;
         }
     }
 
     Combinations {
-        n: n,
+        k: k,
         indices: indices,
         pool: pool,
         first: true,
@@ -52,18 +52,18 @@ impl<I> Iterator for Combinations<I>
     fn next(&mut self) -> Option<Self::Item> {
         let mut pool_len = self.pool.len();
         if self.pool.is_done() {
-            if pool_len == 0 || self.n > pool_len {
+            if pool_len == 0 || self.k > pool_len {
                 return None;
             }
         }
 
         if self.first {
             self.first = false;
-        } else if self.n == 0 {
+        } else if self.k == 0 {
             return None;
         } else {
             // Scan from the end, looking for an index to increment
-            let mut i: usize = self.n - 1;
+            let mut i: usize = self.k - 1;
 
             // Check if we need to consume more from the iterator
             if self.indices[i] == pool_len - 1 && !self.pool.is_done() {
@@ -72,7 +72,7 @@ impl<I> Iterator for Combinations<I>
                 }
             }
 
-            while self.indices[i] == i + pool_len - self.n {
+            while self.indices[i] == i + pool_len - self.k {
                 if i > 0 {
                     i -= 1;
                 } else {
@@ -84,14 +84,14 @@ impl<I> Iterator for Combinations<I>
             // Increment index, and reset the ones to its right
             self.indices[i] += 1;
             let mut j = i + 1;
-            while j < self.n {
+            while j < self.k {
                 self.indices[j] = self.indices[j - 1] + 1;
                 j += 1;
             }
         }
 
         // Create result vector based on the indices
-        let mut result = Vec::with_capacity(self.n);
+        let mut result = Vec::with_capacity(self.k);
         for i in self.indices.iter() {
             result.push(self.pool[*i].clone());
         }

src/combinations_with_replacement.rs

@@ -11,7 +11,7 @@ where
     I: Iterator,
     I::Item: Clone,
 {
-    n: usize,
+    k: usize,
     indices: Vec<usize>,
     // The current known max index value. This increases as pool grows.
     max_index: usize,
@@ -24,7 +24,7 @@ where
     I: Iterator + fmt::Debug,
     I::Item: fmt::Debug + Clone,
 {
-    debug_fmt_fields!(Combinations, n, indices, max_index, pool, first);
+    debug_fmt_fields!(Combinations, k, indices, max_index, pool, first);
 }
 
 impl<I> CombinationsWithReplacement<I>
@@ -39,16 +39,16 @@ where
 }
 
 /// Create a new `CombinationsWithReplacement` from a clonable iterator.
-pub fn combinations_with_replacement<I>(iter: I, n: usize) -> CombinationsWithReplacement<I>
+pub fn combinations_with_replacement<I>(iter: I, k: usize) -> CombinationsWithReplacement<I>
 where
     I: Iterator,
     I::Item: Clone,
 {
-    let indices: Vec<usize> = vec![0; n];
+    let indices: Vec<usize> = vec![0; k];
     let pool: LazyBuffer<I> = LazyBuffer::new(iter);
 
     CombinationsWithReplacement {
-        n,
+        k,
         indices,
         max_index: 0,
         pool: pool,
@@ -66,7 +66,7 @@ where
         // If this is the first iteration, return early
         if self.first {
             // In empty edge cases, stop iterating immediately
-            return if self.n == 0 || self.pool.is_done() {
+            return if self.k == 0 || self.pool.is_done() {
                 None
             // Otherwise, yield the initial state
             } else {

src/lazy_buffer.rs

@@ -2,7 +2,7 @@ use std::ops::Index;
 
 #[derive(Debug, Clone)]
 pub struct LazyBuffer<I: Iterator> {
-    it: I,
+    pub it: I,
     done: bool,
     buffer: Vec<I::Item>,
 }
@@ -54,14 +54,15 @@ where
     }
 }
 
-impl<I> Index<usize> for LazyBuffer<I>
+impl<I, J> Index<J> for LazyBuffer<I>
 where
     I: Iterator,
     I::Item: Sized,
+    Vec<I::Item>: Index<J>
 {
-    type Output = I::Item;
+    type Output = <Vec<I::Item> as Index<J>>::Output;
 
-    fn index<'b>(&'b self, _index: usize) -> &'b I::Item {
+    fn index(&self, _index: J) -> &Self::Output {
         self.buffer.index(_index)
     }
 }

src/lib.rs

@@ -117,6 +117,8 @@ pub mod structs {
     pub use multipeek_impl::MultiPeek;
     pub use pad_tail::PadUsing;
     pub use peeking_take_while::PeekingTakeWhile;
+    #[cfg(feature = "use_std")]
+    pub use permutations::Permutations;
     pub use process_results_impl::ProcessResults;
     #[cfg(feature = "use_std")]
     pub use put_back_n_impl::PutBackN;
@@ -182,6 +184,8 @@ mod minmax;
 mod multipeek_impl;
 mod pad_tail;
 mod peeking_take_while;
+#[cfg(feature = "use_std")]
+mod permutations;
 mod process_results_impl;
 #[cfg(feature = "use_std")]
 mod put_back_n_impl;
@@ -1135,12 +1139,15 @@ pub trait Itertools : Iterator {
         adaptors::tuple_combinations(self)
     }
 
-    /// Return an iterator adaptor that iterates over the `n`-length combinations of
+    /// Return an iterator adaptor that iterates over the `k`-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.
     ///
+    /// If the input iterator is empty, or `k` is 0, or `k` greater than the
+    /// length of the input iterator, the resultant iterator adaptor will be empty.
+    ///
     /// ```
     /// use itertools::Itertools;
     ///
@@ -1150,10 +1157,11 @@ pub trait Itertools : Iterator {
     ///     vec![1, 2, 4],
     ///     vec![1, 3, 4],
     ///     vec![2, 3, 4],
-    ///     ]);
+    /// ]);
     /// ```
     ///
     /// Note: Combinations does not take into account the equality of the iterated values.
+    ///
     /// ```
     /// use itertools::Itertools;
     ///
@@ -1164,16 +1172,15 @@ pub trait Itertools : Iterator {
     ///     vec![2, 2],
     /// ]);
     /// ```
-    ///
     #[cfg(feature = "use_std")]
-    fn combinations(self, n: usize) -> Combinations<Self>
+    fn combinations(self, k: usize) -> Combinations<Self>
         where Self: Sized,
               Self::Item: Clone
     {
-        combinations::combinations(self, n)
+        combinations::combinations(self, k)
     }
 
-    /// Return an iterator that iterates over the `n`-length combinations of
+    /// Return an iterator that iterates over the `k`-length combinations of
     /// the elements from an iterator, with replacement.
     ///
     /// Iterator element type is `Vec<Self::Item>`. The iterator produces a new Vec per iteration,
@@ -1190,15 +1197,61 @@ pub trait Itertools : Iterator {
     ///     vec![2, 2],
     ///     vec![2, 3],
     ///     vec![3, 3],
-    ///     ]);
+    /// ]);
     /// ```
     #[cfg(feature = "use_std")]
-    fn combinations_with_replacement(self, n: usize) -> CombinationsWithReplacement<Self>
+    fn combinations_with_replacement(self, k: usize) -> CombinationsWithReplacement<Self>
     where
         Self: Sized,
         Self::Item: Clone,
     {
-        combinations_with_replacement::combinations_with_replacement(self, n)
+        combinations_with_replacement::combinations_with_replacement(self, k)
+    }
+
+    /// Return an iterator adaptor that iterates over all k-permutations of the
+    /// elements from an iterator.
+    ///
+    /// Iterator element type is `Vec<Self::Item>` with length `k`. The iterator
+    /// produces a new Vec per iteration, and clones the iterator elements.
+    ///
+    /// If `k` is greater than the length of the input iterator, the resultant
+    /// iterator adaptor will be empty.
+    ///
+    /// ```
+    /// use itertools::Itertools;
+    ///
+    /// let perms = (5..8).permutations(2);
+    /// itertools::assert_equal(perms, vec![
+    ///     vec![5, 6],
+    ///     vec![5, 7],
+    ///     vec![6, 5],
+    ///     vec![6, 7],
+    ///     vec![7, 5],
+    ///     vec![7, 6],
+    /// ]);
+    /// ```
+    ///
+    /// Note: Permutations does not take into account the equality of the iterated values.
+    ///
+    /// ```
+    /// use itertools::Itertools;
+    ///
+    /// let it = vec![2, 2].into_iter().permutations(2);
+    /// itertools::assert_equal(it, vec![
+    ///     vec![2, 2], // Note: these are the same
+    ///     vec![2, 2], // Note: these are the same
+    /// ]);
+    ///
+    /// Note: The source iterator is collected lazily, and will not be
+    /// re-iterated if the permutations adaptor is completed and re-iterated.
+    /// ```
+    ///
+    #[cfg(feature = "use_std")]
+    fn permutations(self, k: usize) -> Permutations<Self>
+        where Self: Sized,
+              Self::Item: Clone
+    {
+        permutations::permutations(self, k)
     }
 
     /// Return an iterator adaptor that pads the sequence to a minimum length of
@@ -1997,19 +2050,21 @@ pub trait Itertools : Iterator {
     /// assert_eq!(successes, [1, 2]);
     /// assert_eq!(failures, [false, true]);
     /// ```
-    fn partition_map<A, B, F, L, R>(self, mut predicate: F) -> (A, B)
+    fn partition_map<A, B, F, L, R>(self, predicate: F) -> (A, B)
         where Self: Sized,
-              F: FnMut(Self::Item) -> Either<L, R>,
+              F: Fn(Self::Item) -> Either<L, R>,
               A: Default + Extend<L>,
               B: Default + Extend<R>,
     {
         let mut left = A::default();
         let mut right = B::default();
 
-        self.for_each(|val| match predicate(val) {
-            Either::Left(v) => left.extend(Some(v)),
-            Either::Right(v) => right.extend(Some(v)),
-        });
+        for val in self {
+            match predicate(val) {
+                Either::Left(v) => left.extend(Some(v)),
+                Either::Right(v) => right.extend(Some(v)),
+            }
+        }
 
         (left, right)
     }