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Function std.algorithm.iteration.uniq

Lazily iterates unique consecutive elements of the given range (functionality akin to the uniq system utility). Equivalence of elements is assessed by using the predicate pred, by default "a == b". The predicate is passed to binaryFun, and can either accept a string, or any callable that can be executed via pred(element, element). If the given range is bidirectional, uniq also yields a bidirectional range.

auto uniq(alias pred, Range) (
  Range r
if (isInputRange!Range && is(typeof(binaryFun!pred(r.front, r.front)) == bool));


pred Predicate for determining equivalence between range elements.
r An input range of elements to filter.


An input range of consecutively unique elements in the original range. If r is also a forward range or bidirectional range, the returned range will be likewise.


import std.algorithm.comparison : equal;
import std.algorithm.mutation : copy;

int[] arr = [ 1, 2, 2, 2, 2, 3, 4, 4, 4, 5 ];
assert(equal(uniq(arr), [ 1, 2, 3, 4, 5 ][]));

// Filter duplicates in-place using copy
arr.length -= arr.uniq().copy(arr).length;
writeln(arr); // [1, 2, 3, 4, 5]

// Note that uniqueness is only determined consecutively; duplicated
// elements separated by an intervening different element will not be
// eliminated:
assert(equal(uniq([ 1, 1, 2, 1, 1, 3, 1]), [1, 2, 1, 3, 1]));


Andrei Alexandrescu


Boost License 1.0.