按键值推力过滤 [英] Thrust filter by key value

问题描述

在我的应用程序中，我有一个类如下：

In my application I have a class like this:

class sample{
    thrust::device_vector<int>   edge_ID;
    thrust::device_vector<float> weight;
    thrust::device_vector<int>   layer_ID;

/*functions, zip_iterators etc. */

};

在给定的索引处，每个向量存储相同边缘的相应数据。

At a given index every vector stores the corresponding data of the same edge.

我想编写一个过滤掉给定图层所有边缘的函数，如下所示：

I want to write a function that filters out all the edges of a given layer, something like this:

void filter(const sample& src, sample& dest, const int& target_layer){
      for(...){
        if( src.layer_ID[x] == target_layer)/*copy values to dest*/;
      }
}

我发现最好的方法是使用 thrust :: copy_if（...） （详情）

The best way I've found to do this is by using thrust::copy_if(...) (details)

看起来像这样：

void filter(const sample& src, sample& dest, const int& target_layer){
     thrust::copy_if(src.begin(),
                     src.end(),
                     dest.begin(),
                     comparing_functor() );
}

这是我们遇到问题的地方：

comparing_functor（）是一个一元函数，这意味着我不能通过我的 target_layer

The comparing_functor() is an unary function, which means I cant pass my target_layer value to it.

任何人都知道如何解决这个问题，或有一个想法来实现这一点，同时保持类的数据结构完整？

Anyone knows how to get around this, or has an idea for implementing this while keeping the data structure of the class intact?

推荐答案

您可以将特定值传递给函子，以便在谓词测试中使用，除了通常传递给他们的数据。这里有一个工作示例：

You can pass specific values to functors for use in the predicate test in addition to the data that is ordinarily passed to them. Here's a worked example:

#include <iostream>
#include <thrust/host_vector.h>
#include <thrust/device_vector.h>
#include <thrust/sequence.h>
#include <thrust/copy.h>

#define DSIZE 10
#define FVAL 5

struct test_functor
{
  const int a;

  test_functor(int _a) : a(_a) {}

  __device__
  bool operator()(const int& x ) {
    return (x==a);
    }
};

int main(){
  int target_layer = FVAL;
  thrust::host_vector<int> h_vals(DSIZE);
  thrust::sequence(h_vals.begin(), h_vals.end());
  thrust::device_vector<int> d_vals = h_vals;
  thrust::device_vector<int> d_result(DSIZE);
  thrust::copy_if(d_vals.begin(), d_vals.end(), d_result.begin(),  test_functor(target_layer));
  thrust::host_vector<int> h_result = d_result;
  std::cout << "Data :" << std::endl;
  thrust::copy(h_vals.begin(), h_vals.end(), std::ostream_iterator<int>( std::cout, " "));
  std::cout << std::endl;
  std::cout << "Filter Value: " << target_layer << std::endl;
  std::cout << "Results :" << std::endl;
  thrust::copy(h_result.begin(), h_result.end(), std::ostream_iterator<int>( std::cout, " "));
  std::cout << std::endl;
  return 0;
}

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