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Introduce the partition_dedup/by/by_key methods for slices

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This commit is contained in:
Clément Renault 2018-09-08 15:33:02 +02:00
parent 7714c430ae
commit 78bccb3540
4 changed files with 237 additions and 5 deletions
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10
src/liballoc/vec.rs
View file

@ -947,10 +947,9 @@ impl<T> Vec<T> {
/// Removes all but the first of consecutive elements in the vector satisfying a given equality
/// relation.
///
/// The `same_bucket` function is passed references to two elements from the vector, and
/// returns `true` if the elements compare equal, or `false` if they do not. The elements are
/// passed in opposite order from their order in the vector, so if `same_bucket(a, b)` returns
/// `true`, `a` is removed.
/// The `same_bucket` function is passed references to two elements from the vector and
/// must determine if the elements compare equal. The elements are passed in opposite order
/// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
///
/// If the vector is sorted, this removes all duplicates.
///
@ -1533,7 +1532,8 @@ impl<'a> Drop for SetLenOnDrop<'a> {
}
impl<T: PartialEq> Vec<T> {
/// Removes consecutive repeated elements in the vector.
/// Removes consecutive repeated elements in the vector according to the
/// [`PartialEq`] trait implementation.
///
/// If the vector is sorted, this removes all duplicates.
///

172
src/libcore/slice/mod.rs
View file

@ -1402,6 +1402,178 @@ impl<T> [T] {
sort::quicksort(self, |a, b| f(a).lt(&f(b)));
}
/// Moves all consecutive repeated elements to the end of the slice according to the
/// [`PartialEq`] trait implementation.
///
/// Returns two slices. The first contains no consecutive repeated elements.
/// The second contains all the duplicates in no specified order.
///
/// If the slice is sorted, the first returned slice contains no duplicates.
///
/// # Examples
///
/// ```
/// #![feature(slice_partition_dedup)]
///
/// let mut slice = [1, 2, 2, 3, 3, 2, 1, 1];
///
/// let (dedup, duplicates) = slice.partition_dedup();
///
/// assert_eq!(dedup, [1, 2, 3, 2, 1]);
/// assert_eq!(duplicates, [2, 3, 1]);
/// ```
#[unstable(feature = "slice_partition_dedup", issue = "54279")]
#[inline]
pub fn partition_dedup(&mut self) -> (&mut [T], &mut [T])
where T: PartialEq
{
self.partition_dedup_by(|a, b| a == b)
}
/// Moves all but the first of consecutive elements to the end of the slice satisfying
/// a given equality relation.
///
/// Returns two slices. The first contains no consecutive repeated elements.
/// The second contains all the duplicates in no specified order.
///
/// The `same_bucket` function is passed references to two elements from the slice and
/// must determine if the elements compare equal. The elements are passed in opposite order
/// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is moved
/// at the end of the slice.
///
/// If the slice is sorted, the first returned slice contains no duplicates.
///
/// # Examples
///
/// ```
/// #![feature(slice_partition_dedup)]
///
/// let mut slice = ["foo", "Foo", "BAZ", "Bar", "bar", "baz", "BAZ"];
///
/// let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.eq_ignore_ascii_case(b));
///
/// assert_eq!(dedup, ["foo", "BAZ", "Bar", "baz"]);
/// assert_eq!(duplicates, ["bar", "Foo", "BAZ"]);
/// ```
#[unstable(feature = "slice_partition_dedup", issue = "54279")]
#[inline]
pub fn partition_dedup_by<F>(&mut self, mut same_bucket: F) -> (&mut [T], &mut [T])
where F: FnMut(&mut T, &mut T) -> bool
{
// Although we have a mutable reference to `self`, we cannot make
// *arbitrary* changes. The `same_bucket` calls could panic, so we
// must ensure that the slice is in a valid state at all times.
//
// The way that we handle this is by using swaps; we iterate
// over all the elements, swapping as we go so that at the end
// the elements we wish to keep are in the front, and those we
// wish to reject are at the back. We can then split the slice.
// This operation is still O(n).
//
// Example: We start in this state, where `r` represents "next
// read" and `w` represents "next_write`.
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 1 | 2 | 3 | 3 |
// +---+---+---+---+---+---+
// w
//
// Comparing self[r] against self[w-1], this is not a duplicate, so
// we swap self[r] and self[w] (no effect as r==w) and then increment both
// r and w, leaving us with:
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 1 | 2 | 3 | 3 |
// +---+---+---+---+---+---+
// w
//
// Comparing self[r] against self[w-1], this value is a duplicate,
// so we increment `r` but leave everything else unchanged:
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 1 | 2 | 3 | 3 |
// +---+---+---+---+---+---+
// w
//
// Comparing self[r] against self[w-1], this is not a duplicate,
// so swap self[r] and self[w] and advance r and w:
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 2 | 1 | 3 | 3 |
// +---+---+---+---+---+---+
// w
//
// Not a duplicate, repeat:
//
// r
// +---+---+---+---+---+---+
// | 0 | 1 | 2 | 3 | 1 | 3 |
// +---+---+---+---+---+---+
// w
//
// Duplicate, advance r. End of slice. Split at w.
let len = self.len();
if len <= 1 {
return (self, &mut [])
}
let ptr = self.as_mut_ptr();
let mut next_read: usize = 1;
let mut next_write: usize = 1;
unsafe {
// Avoid bounds checks by using raw pointers.
while next_read < len {
let ptr_read = ptr.add(next_read);
let prev_ptr_write = ptr.add(next_write - 1);
if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
if next_read != next_write {
let ptr_write = prev_ptr_write.offset(1);
mem::swap(&mut *ptr_read, &mut *ptr_write);
}
next_write += 1;
}
next_read += 1;
}
}
self.split_at_mut(next_write)
}
/// Moves all but the first of consecutive elements to the end of the slice that resolve
/// to the same key.
///
/// Returns two slices. The first contains no consecutive repeated elements.
/// The second contains all the duplicates in no specified order.
///
/// If the slice is sorted, the first returned slice contains no duplicates.
///
/// # Examples
///
/// ```
/// #![feature(slice_partition_dedup)]
///
/// let mut slice = [10, 20, 21, 30, 30, 20, 11, 13];
///
/// let (dedup, duplicates) = slice.partition_dedup_by_key(|i| *i / 10);
///
/// assert_eq!(dedup, [10, 20, 30, 20, 11]);
/// assert_eq!(duplicates, [21, 30, 13]);
/// ```
#[unstable(feature = "slice_partition_dedup", issue = "54279")]
#[inline]
pub fn partition_dedup_by_key<K, F>(&mut self, mut key: F) -> (&mut [T], &mut [T])
where F: FnMut(&mut T) -> K,
K: PartialEq,
{
self.partition_dedup_by(|a, b| key(a) == key(b))
}
/// Rotates the slice in-place such that the first `mid` elements of the
/// slice move to the end while the last `self.len() - mid` elements move to
/// the front. After calling `rotate_left`, the element previously at index

1
src/libcore/tests/lib.rs
View file

@ -39,6 +39,7 @@
#![feature(inner_deref)]
#![feature(slice_internals)]
#![feature(option_replace)]
#![feature(slice_partition_dedup)]
#![feature(copy_within)]
extern crate core;

59
src/libcore/tests/slice.rs
View file

@ -1001,6 +1001,65 @@ fn test_align_to_empty_mid() {
}
}
#[test]
fn test_slice_partition_dedup_by() {
let mut slice: [i32; 9] = [1, -1, 2, 3, 1, -5, 5, -2, 2];
let (dedup, duplicates) = slice.partition_dedup_by(|a, b| a.abs() == b.abs());
assert_eq!(dedup, [1, 2, 3, 1, -5, -2]);
assert_eq!(duplicates, [5, -1, 2]);
}
#[test]
fn test_slice_partition_dedup_empty() {
let mut slice: [i32; 0] = [];
let (dedup, duplicates) = slice.partition_dedup();
assert_eq!(dedup, []);
assert_eq!(duplicates, []);
}
#[test]
fn test_slice_partition_dedup_one() {
let mut slice = [12];
let (dedup, duplicates) = slice.partition_dedup();
assert_eq!(dedup, [12]);
assert_eq!(duplicates, []);
}
#[test]
fn test_slice_partition_dedup_multiple_ident() {
let mut slice = [12, 12, 12, 12, 12, 11, 11, 11, 11, 11, 11];
let (dedup, duplicates) = slice.partition_dedup();
assert_eq!(dedup, [12, 11]);
assert_eq!(duplicates, [12, 12, 12, 12, 11, 11, 11, 11, 11]);
}
#[test]
fn test_slice_partition_dedup_partialeq() {
#[derive(Debug)]
struct Foo(i32, i32);
impl PartialEq for Foo {
fn eq(&self, other: &Foo) -> bool {
self.0 == other.0
}
}
let mut slice = [Foo(0, 1), Foo(0, 5), Foo(1, 7), Foo(1, 9)];
let (dedup, duplicates) = slice.partition_dedup();
assert_eq!(dedup, [Foo(0, 1), Foo(1, 7)]);
assert_eq!(duplicates, [Foo(0, 5), Foo(1, 9)]);
}
#[test]
fn test_copy_within() {
// Start to end, with a RangeTo.