thrust

◆ unique_by_key() [3/4]

template<typename DerivedPolicy , typename ForwardIterator1 , typename ForwardIterator2 , typename BinaryPredicate >
__host__ __device__ thrust::pair<ForwardIterator1,ForwardIterator2> thrust::unique_by_key ( const thrust::detail::execution_policy_base< DerivedPolicy > &  exec,
ForwardIterator1  keys_first,
ForwardIterator1  keys_last,
ForwardIterator2  values_first,
BinaryPredicate  binary_pred 
)

unique_by_key is a generalization of unique to key-value pairs. For each group of consecutive keys in the range [keys_first, keys_last) that are equal, unique_by_key removes all but the first element of the group. Similarly, the corresponding values in the range [values_first, values_first + (keys_last - keys_first)) are also removed.

This version of unique_by_key uses the function object binary_pred to test for equality and project1st to reduce values with equal keys.

The algorithm's execution is parallelized as determined by exec.

Parameters
execThe execution policy to use for parallelization.
keys_firstThe beginning of the key range.
keys_lastThe end of the key range.
values_firstThe beginning of the value range.
binary_predThe binary predicate used to determine equality.
Returns
The end of the unique range [first, new_last).
Template Parameters
DerivedPolicyThe name of the derived execution policy.
ForwardIterator1is a model of Forward Iterator, and ForwardIterator1 is mutable, and ForwardIterator's value_type is a model of Equality Comparable.
ForwardIterator2is a model of Forward Iterator, and ForwardIterator2 is mutable.
BinaryPredicateis a model of Binary Predicate.
Precondition
The range [keys_first, keys_last) and the range [values_first, values_first + (keys_last - keys_first)) shall not overlap.

The following code snippet demonstrates how to use unique_by_key to compact a sequence of key/value pairs to remove consecutive duplicates using the thrust::host execution policy for parallelization:

#include <thrust/unique.h>
...
const int N = 7;
int A[N] = {1, 3, 3, 3, 2, 2, 1}; // keys
int B[N] = {9, 8, 7, 6, 5, 4, 3}; // values
new_end = thrust::unique_by_key(thrust::host, keys, keys + N, values, binary_pred);
// The first four keys in A are now {1, 3, 2, 1} and new_end.first - A is 4.
// The first four values in B are now {9, 8, 5, 3} and new_end.second - B is 4.
See also
unique
unique_by_key_copy
reduce_by_key