Template Function thrust::reduce_by_key(InputIterator1, InputIterator1, InputIterator2, OutputIterator1, OutputIterator2, BinaryPredicate, BinaryFunction)¶
Function Documentation¶
-
template<typename
InputIterator1
, typenameInputIterator2
, typenameOutputIterator1
, typenameOutputIterator2
, typenameBinaryPredicate
, typenameBinaryFunction
>
thrust::pair<OutputIterator1, OutputIterator2>thrust
::
reduce_by_key
(InputIterator1 keys_first, InputIterator1 keys_last, InputIterator2 values_first, OutputIterator1 keys_output, OutputIterator2 values_output, BinaryPredicate binary_pred, BinaryFunction binary_op) reduce_by_key
is a generalization ofreduce
to key-value pairs. For each group of consecutive keys in the range[keys_first, keys_last)
that are equal,reduce_by_key
copies the first element of the group to thekeys_output
. The corresponding values in the range are reduced using theBinaryFunction
binary_op
and the result copied tovalues_output
. Specifically, if consecutive key iteratorsi
and(i + 1) are such that
binary_pred(*i, *(i+1))
istrue
, then the corresponding values are reduced to a single value withbinary_op
.This version of
reduce_by_key
uses the function objectbinary_pred
to test for equality andbinary_op
to reduce values with equal keys.The following code snippet demonstrates how to use
reduce_by_key
to compact a sequence of key/value pairs and sum values with equal keys.- Return
A pair of iterators at end of the ranges
[keys_output, keys_output_last)
and[values_output, values_output_last)
.- Pre
The input ranges shall not overlap either output range.
- Parameters
keys_first
: The beginning of the input key range.keys_last
: The end of the input key range.values_first
: The beginning of the input value range.keys_output
: The beginning of the output key range.values_output
: The beginning of the output value range.binary_pred
: The binary predicate used to determine equality.binary_op
: The binary function used to accumulate values.
- Template Parameters
InputIterator1
: is a model of Input Iterator,InputIterator2
: is a model of Input Iterator,OutputIterator1
: is a model of Output Iterator and andInputIterator1's
value_type
is convertible toOutputIterator1's
value_type
.OutputIterator2
: is a model of Output Iterator and andInputIterator2's
value_type
is convertible toOutputIterator2's
value_type
.BinaryPredicate
: is a model of Binary Predicate.BinaryFunction
: is a model of Binary Function andBinaryFunction's
result_type
is convertible toOutputIterator2's
value_type
.
#include <thrust/reduce.h> ... const int N = 7; int A[N] = {1, 3, 3, 3, 2, 2, 1}; // input keys int B[N] = {9, 8, 7, 6, 5, 4, 3}; // input values int C[N]; // output keys int D[N]; // output values thrust::pair<int*,int*> new_end; thrust::equal_to<int> binary_pred; thrust::plus<int> binary_op; new_end = thrust::reduce_by_key(A, A + N, B, C, D, binary_pred, binary_op); // The first four keys in C are now {1, 3, 2, 1} and new_end.first - C is 4. // The first four values in D are now {9, 21, 9, 3} and new_end.second - D is 4.
- See
reduce
- See
unique_copy
- See
unique_by_key
- See
unique_by_key_copy