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# std::stable_partition

From cppreference.com
< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
template< class BidirIt, class UnaryPredicate > BidirIt stable_partition( BidirIt first, BidirIt last, UnaryPredicate p ); |  |

Reorders the elements in the range `[first, last)` in such a way that all elements for which the predicate `p` returns true precede the elements for which predicate `p` returns false. Relative order of the elements is preserved.

### [edit] Parameters

first, last | - | the range of elements to reorder
p | - | unary predicate which returns ​true if the element should be ordered before other elements. The signature of the predicate function should be equivalent to the following: bool pred(const Type &a); The signature does not need to have const &, but the function must not modify the objects passed to it. The type Type must be such that an object of type BidirIt can be dereferenced and then implicitly converted to Type. ​
Type requirements
- `BidirIt` must meet the requirements of `ValueSwappable` and `BidirectionalIterator`.
- The type of dereferenced `BidirIt` must meet the requirements of `MoveAssignable` and `MoveConstructible`.
- `UnaryPredicate` must meet the requirements of `Predicate`.

### [edit] Return value

Iterator to the first element of the second group

### [edit] Complexity

Exactly `last-first` applications of the predicate and at most `(last-first)*log(last-first)` swaps if there is insufficient memory or linear number of swaps if sufficient memory is available.

### [edit] Example

Run this code

    #include <iostream>
    #include <algorithm>
    #include <vector>

    int main()
    {
        std::vector<int> v{0, 0, 3, 0, 2, 4, 5, 0, 7};
        std::stable_partition(v.begin(), v.end(), [](int n){return n>0;});
        for (int n : v) {
            std::cout << n << ' ';
        }
        std::cout << '\n';
    }

Output:

    3 2 4 5 7 0 0 0 0

### [edit] See also

partition | divides a range of elements into two groups (function template) [edit]

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