Template Function thrust::set_difference_by_key(InputIterator1, InputIterator1, InputIterator2, InputIterator2, InputIterator3, InputIterator4, OutputIterator1, OutputIterator2)

Function Documentation

template<typename InputIterator1, typename InputIterator2, typename InputIterator3, typename InputIterator4, typename OutputIterator1, typename OutputIterator2>
thrust::pair<OutputIterator1, OutputIterator2> thrust::set_difference_by_key(InputIterator1 keys_first1, InputIterator1 keys_last1, InputIterator2 keys_first2, InputIterator2 keys_last2, InputIterator3 values_first1, InputIterator4 values_first2, OutputIterator1 keys_result, OutputIterator2 values_result)

set_difference_by_key performs a key-value difference operation from set theory. set_difference_by_key constructs a sorted range that is the difference of the sorted ranges [keys_first1, keys_last1) and [keys_first2, keys_last2). Associated with each element from the input and output key ranges is a value element. The associated input value ranges need not be sorted.

In the simplest case, set_difference_by_key performs the “difference” operation from set theory: the keys output range contains a copy of every element that is contained in [keys_first1, keys_last1) and not contained in [keys_first2, keys_last2). The general case is more complicated, because the input ranges may contain duplicate elements. The generalization is that if [keys_first1, keys_last1) contains m elements that are equivalent to each other and if [keys_first2, keys_last2) contains n elements that are equivalent to them, the last max(m-n,0) elements from [keys_first1, keys_last1) range shall be copied to the output range.

Each time a key element is copied from [keys_first1, keys_last1) or [keys_first2, keys_last2) is copied to the keys output range, the corresponding value element is copied from the corresponding values input range (beginning at values_first1 or values_first2) to the values output range.

This version of set_difference_by_key compares key elements using operator<.

The following code snippet demonstrates how to use

set_difference_by_key to compute the set difference of two sets of integers sorted in ascending order with their values.
Return

A pair p such that p.first is the end of the output range of keys, and such that p.second is the end of the output range of values.

Pre

The ranges [keys_first1, keys_last1) and [keys_first2, keys_last2) shall be sorted with respect to operator<.

Pre

The resulting ranges shall not overlap with any input range.

Parameters

  • keys_first1: The beginning of the first input range of keys.

  • keys_last1: The end of the first input range of keys.

  • keys_first2: The beginning of the second input range of keys.

  • keys_last2: The end of the second input range of keys.

  • values_first1: The beginning of the first input range of values.

  • values_first2: The beginning of the first input range of values.

  • keys_result: The beginning of the output range of keys.

  • values_result: The beginning of the output range of values.

Template Parameters

  • InputIterator1: is a model of Input Iterator, InputIterator1 and InputIterator2 have the same value_type, InputIterator1's value_type is a model of LessThan Comparable, the ordering on InputIterator1's value_type is a strict weak ordering, as defined in the LessThan Comparable requirements, and InputIterator1's value_type is convertable to a type in OutputIterator's set of value_types.

  • InputIterator2: is a model of Input Iterator, InputIterator2 and InputIterator1 have the same value_type, InputIterator2's value_type is a model of LessThan Comparable, the ordering on InputIterator2's value_type is a strict weak ordering, as defined in the LessThan Comparable requirements, and InputIterator2's value_type is convertable to a type in OutputIterator's set of value_types.

  • InputIterator3: is a model of Input Iterator, and InputIterator3's value_type is convertible to a type in OutputIterator2's set of value_types.

  • InputIterator4: is a model of Input Iterator, and InputIterator4's value_type is convertible to a type in OutputIterator2's set of value_types.

  • OutputIterator1: is a model of Output Iterator.

  • OutputIterator2: is a model of Output Iterator.

#include <thrust/set_operations.h>
...
int A_keys[6] = {0, 1, 3, 4, 5, 6, 9};
int A_vals[6] = {0, 0, 0, 0, 0, 0, 0};

int B_keys[5] = {1, 3, 5, 7, 9};
int B_vals[5] = {1, 1, 1, 1, 1};

int keys_result[3];
int vals_result[3];

thrust::pair<int*,int*> end = thrust::set_difference_by_key(A_keys, A_keys + 6, B_keys, B_keys + 5, A_vals, B_vals, keys_result, vals_result);
// keys_result is now {0, 4, 6}
// vals_result is now {0, 0, 0}

See

set_union_by_key

See

set_intersection_by_key

See

set_symmetric_difference_by_key

See

sort_by_key

See

is_sorted