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Difference between revisions of "cpp/algorithm/is partitioned"

From cppreference.com
< cpp‎ | algorithm
(p0467r2 (iterator categories for parallel algos))
(Uses {{mark constexpr since c++20}}.)
 
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{{cpp/algorithm/navbar}}
 
{{cpp/algorithm/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
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{{dcl header | algorithm}}
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{{dcl header|algorithm}}
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{{dcl | since=c++11 | num= 1 |1=
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{{dcl|num=1|since=c++11|notes={{mark constexpr since c++20}}|
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template< class InputIt, class UnaryPredicate >
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template< class InputIt, class UnaryPred >
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bool is_partitioned( InputIt first, InputIt last, UnaryPredicate p );
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bool is_partitioned( InputIt first, InputIt last, UnaryPred p );
 +
}}
 +
{{dcl|num=2|since=c++17|
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template< class ExecutionPolicy, class ForwardIt, class UnaryPred >
 +
bool is_partitioned( ExecutionPolicy&& policy,
 +
                    ForwardIt first, ForwardIt last, UnaryPred p );
 
}}
 
}}
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{{dcl | since=c++17 | num= 2 |1=
 
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template< class ExecutionPolicy, class ForwardIt, class UnaryPredicate >
 
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bool is_partitioned( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, UnaryPredicate p );}}
 
 
{{dcl end}}
 
{{dcl end}}
  
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@1@ Returns {{c|true}} if all elements in the range {{tt|[first, last)}} that satisfy the predicate {{tt|p}} appear before all elements that don't. Also returns {{c|true}} if {{tt|[first, last)}} is empty.
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@1@ Checks whether {{range|first|last}} is partitioned by the predicate {{c|p}}: all elements satisfy {{c|p}} appear before all elements that do not.
  
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@2@ Same as {{v|1}}, but executed according to {{tt|policy}}. {{cpp/enable_if| {{c|std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>}} is true}}
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@2@ Same as {{v|1}}, but executed according to {{c|policy}}.
 +
@@ {{cpp/algorithm/parallel overload precondition}}
  
 
===Parameters===
 
===Parameters===
 
{{par begin}}
 
{{par begin}}
−
{{par | first, last | the range of elements to check}}
+
{{par|first, last|the range of elements to check}}
 
{{par exec pol}}
 
{{par exec pol}}
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{{par pred1 | p | for the elements expected to be found in the beginning of the range | p1=InputIt}}
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{{par pred1|p|for the elements expected to be found in the beginning of the range|p1=InputIt}}
 
{{par hreq}}
 
{{par hreq}}
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{{par req concept | InputIt | InputIterator}}
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{{par req named|InputIt|InputIterator}}
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{{par req concept | ForwardIt | ForwardIterator}}
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{{par req named|ForwardIt|ForwardIterator|notes=and its value type must be convertible to {{tt|UnaryPred}}'s parameter type.}}
−
{{par req concept | UnaryPredicate | Predicate}}
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{{par req named|UnaryPred|Predicate}}
 
{{par end}}
 
{{par end}}
  
 
===Return value===
 
===Return value===
−
 
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{{c|true}} if the elements {{c|e}} of {{range|first|last}} are {{rlp|/#Requirements|partitioned}} with respect to the expression {{c|p(e)}}. {{c|false}} otherwise.
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{{c|true}} if the range {{tt|[first, last)}} is empty or is partitioned by {{tt|p}}. {{c|false}} otherwise.
+
  
 
===Complexity===
 
===Complexity===
−
 
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At most {{c|std::distance(first, last)}} applications of {{c|p}}.
−
At most {{tt|std::distance(first, last)}} applications of {{tt|p}}.
+
  
 
===Exceptions===
 
===Exceptions===
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{{cpp/algorithm/parallel_exceptions_reporting_behavior|singular=yes}}
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{{cpp/algorithm/parallel exceptions reporting behavior|singular=yes}}
  
 
===Possible implementation===
 
===Possible implementation===
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{{eq fun | 1=
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{{eq fun|1=
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template< class InputIt, class UnaryPredicate >
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template<class InputIt, class UnaryPred>
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bool is_partitioned(InputIt first, InputIt last, UnaryPredicate p)
+
bool is_partitioned(InputIt first, InputIt last, UnaryPred p)
 
{
 
{
 
     for (; first != last; ++first)
 
     for (; first != last; ++first)
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===Example===
 
===Example===
 
{{example
 
{{example
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|
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|
−
| code=
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|code=
 
#include <algorithm>
 
#include <algorithm>
 
#include <array>
 
#include <array>
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int main()
 
int main()
 
{
 
{
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     std::array<int, 9> v = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
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     std::array<int, 9> v {1, 2, 3, 4, 5, 6, 7, 8, 9};
 
      
 
      
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     auto is_even = [](int i){ return i % 2 == 0; };
+
     auto is_even = [](int i) { return i % 2 == 0; };
 
     std::cout.setf(std::ios_base::boolalpha);
 
     std::cout.setf(std::ios_base::boolalpha);
 
     std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' ';
 
     std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' ';
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     std::reverse(v.begin(), v.end());
 
     std::reverse(v.begin(), v.end());
−
     std::cout << std::is_partitioned(v.begin(), v.end(), is_even);
+
     std::cout << std::is_partitioned(v.cbegin(), v.cend(), is_even) << ' ';
 +
    std::cout << std::is_partitioned(v.crbegin(), v.crend(), is_even) << '\n';
 
}
 
}
−
| output=
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|output=
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false true false
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false true false true
 
}}
 
}}
  
 
===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
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{{dsc inc | cpp/algorithm/dsc partition}}
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{{dsc inc|cpp/algorithm/dsc partition}}
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{{dsc inc | cpp/algorithm/dsc partition_point}}
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{{dsc inc|cpp/algorithm/dsc partition_point}}
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{{dsc inc|cpp/algorithm/ranges/dsc is_partitioned}}
 
{{dsc end}}
 
{{dsc end}}
  
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[[de:cpp/algorithm/is partitioned]]
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{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
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[[es:cpp/algorithm/is partitioned]]
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[[it:cpp/algorithm/is partitioned]]
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[[ja:cpp/algorithm/is partitioned]]
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[[zh:cpp/algorithm/is partitioned]]
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Latest revision as of 01:54, 28 March 2024

 
C++
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
is_partitioned
(C++11)
(C++11)

Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
Defined in header <algorithm>
template< class InputIt, class UnaryPred >
bool is_partitioned( InputIt first, InputIt last, UnaryPred p );
 (1) (since C++11)
(constexpr since C++20)
template< class ExecutionPolicy, class ForwardIt, class UnaryPred >

bool is_partitioned( ExecutionPolicy&& policy,

                     ForwardIt first, ForwardIt last, UnaryPred p );
 (2) (since C++17)
1) Checks whether [first, last) is partitioned by the predicate p: all elements satisfy p appear before all elements that do not.
2) Same as (1), but executed according to policy.
This overload participates in overload resolution only if

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

(until C++20)

std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.

(since C++20)

Contents

[edit] Parameters

first, last - the range of elements to check
policy - the execution policy to use. See execution policy for details.
p - unary predicate which returns ​true for the elements expected to be found in the beginning of the range.

The expression p(v) must be convertible to bool for every argument v of type (possibly const) VT, where VT is the value type of InputIt, regardless of value category, and must not modify v. Thus, a parameter type of VT&is not allowed, nor is VT unless for VT a move is equivalent to a copy(since C++11). ​

Type requirements
-
InputIt must meet the requirements of LegacyInputIterator.
-
ForwardIt must meet the requirements of LegacyForwardIterator. and its value type must be convertible to UnaryPred's parameter type.
-
UnaryPred must meet the requirements of Predicate.

[edit] Return value

true if the elements e of [first, last) are partitioned with respect to the expression p(e). false otherwise.

[edit] Complexity

At most std::distance(first, last) applications of p.

[edit] Exceptions

The overload with a template parameter named ExecutionPolicy reports errors as follows:

  • If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

[edit] Possible implementation

template<class InputIt, class UnaryPred>
bool is_partitioned(InputIt first, InputIt last, UnaryPred p)
{
    for (; first != last; ++first)
        if (!p(*first))
            break;
    for (; first != last; ++first)
        if (p(*first))
            return false;
    return true;
}

[edit] Example

Run this code
#include <algorithm>
#include <array>
#include <iostream>
 
int main()
{
    std::array<int, 9> v {1, 2, 3, 4, 5, 6, 7, 8, 9};
 
    auto is_even = [](int i) { return i % 2 == 0; };
    std::cout.setf(std::ios_base::boolalpha);
    std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' ';
 
    std::partition(v.begin(), v.end(), is_even);
    std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' ';
 
    std::reverse(v.begin(), v.end());
    std::cout << std::is_partitioned(v.cbegin(), v.cend(), is_even) << ' ';
    std::cout << std::is_partitioned(v.crbegin(), v.crend(), is_even) << '\n';
}

Output: 

false true false true

[edit] See also

 divides a range of elements into two groups
(function template) [edit]
(C++11)
 locates the partition point of a partitioned range
(function template) [edit]
(C++20)
 determines if the range is partitioned by the given predicate
(niebloid)[edit]
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