std::unique_copy

 

C++

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Algorithm library

Functions
Non-modifying sequence operations
all_of any_of none_of (C++11) (C++11) (C++11) for_each count count_if mismatch equal	find find_if find_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copy copy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n remove remove_if remove_copy remove_copy_if	replace replace_if replace_copy replace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffle shuffle   (C++11) unique unique_copy
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is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
Sorting operations (on sorted ranges)
is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
Binary search operations (on sorted ranges)
lower_bound upper_bound	binary_search equal_range
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merge inplace_merge includes	set_difference set_intersection set_symmetric_difference set_union
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is_heap is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
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max max_element min min_element minmax (C++11) minmax_element (C++11)	lexicographical_compare is_permutation (C++11) next_permutation prev_permutation
Numeric operations
iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

Defined in header <algorithm>
template< class InputIt, class OutputIt > ForwardIt unique_copy( InputIt first, InputIt last,                        OutputIt d_first );	(1)
template< class InputIt, class OutputIt, class BinaryPredicate > ForwardIt unique_copy( InputIt first, InputIt last,                        OutputIt d_first, BinaryPredicate p );	(2)

Copies the elements from the range [first, last), to another range beginning at d_first in such a way that there are no consecutive equal elements. Only the first element of each group of equal elements is copied. The first version uses operator== to compare the elements, the second version uses the given binary predicate p.

Parameters

first, last	-	the range of elements to process
d_first	-	the beginning of the destination range
p	-	binary predicate which returns ​true if the elements should be treated as equal. The signature of the predicate function should be equivalent to the following: bool pred(const Type1 &a, const Type2 &b); The signature does not need to have const &, but the function must not modify the objects passed to it. The types  Type1 and  Type2 must be such that an object of type ForwardIt can be dereferenced and then implicitly converted to both of them. ​
Type requirements
- InputIt must meet the requirements of InputIterator.
- OutputIt must meet the requirements of OutputIterator.
- The type of dereferenced InputIt must meet the requirements of CopyAssignable.
- The type of dereferenced InputIt must meet the requirements of CopyConstructible. if neither InputIt nor OutputIt satisfies ForwardIterator

Return value

Output iterator to the element past the last written element

Possible implementation

First version
template<class ForwardIt, class OutputIt> ForwardIt unique_copy(ForwardIt first, ForwardIt last, OutputIt d_first) {   if (first == last) return d_first;   *d_first = *first; while (++first != last) { if (!(*d_first == *first)) { *(++d_first) = *first; } } return ++d_first; }
Second version
template<class ForwardIt, class OutputIt, class BinaryPredicate> ForwardIt unique_copy(ForwardIt first, ForwardIt last, OutputIt d_first, BinaryPredicate p) {   if (first == last) return d_first;   *d_first = *first; while (++first != last) { if (!p(*result, *first)) { *(++d_first) = *first; } } return ++d_first; }

Example

The following program trims all multiple consecutive spaces in a const string and prints the result

run this code

#include <string>
#include <iostream>
#include <algorithm>
#include <iterator>
 
int main()
{
    std::string s1 = "The      string    with many       spaces!";
    std::cout << "before: " << s1 << '\n';
 
    std::string s2;
    std::unique_copy(s1.begin(), s1.end(), std::back_inserter(s2),
                     [](char c1, char c2){ return c1 == ' ' && c2 == ' '; });
 
    std::cout << "after:  " << s2 << '\n';
}

Output:

before: The      string    with many       spaces!
after:  The string with many spaces!

Complexity

linear in the distance between first and last

See also

adjacent_find	finds two identical (or some other relationship) items adjacent to each other (function template)
unique	removes consecutive duplicate elements in a range (function template)