推力计数发生 [英] thrust count occurence

问题描述

可能重复：

计算cuda数组中出现的数字

有没有办法使用thrust或cuda来计算数组中重复项的出现次数？

is there a way to use thrust or cuda to count occurrence for the duplicates in an array?

例如
如果我有一个设备向量{ 11，9，1，3，11，1，2，9，1，11}
我应该得到1：3 2：1 3：1 9：2,11：4

for example if I have a device vector { 11, 11, 9, 1, 3, 11, 1, 2, 9, 1, 11} I should get 1 :3 2:1 3:1 9:2, 11:4

如果推力不能做，那我该如何使用内核呢？

if thrust cannot do that, How can I use a kernel to do that?

谢谢！我在做浓度计算。这就是为什么我问这个问题。
假设在域中存在100000个具有nx X ny X nz个单元格的粒子，我需要计算每个单元格的浓度（每个单元格中有多少粒子）

Thanks! I am doing concentration calculation. that's why I am asking this question. assume there are 100000 particles in the domain which has nx X ny X nz cells, i need to calculate the concentration of each cell(how many particles in each cell)

我的内核是这个

__global__ void concentration_kernel(float3* posPtr, uint* device_cons) 
{
    __shared__ uint cache[256];
    uint x = threadIdx.x + blockIdx.x * blockDim.x;
    uint y = threadIdx.y + blockIdx.y * blockDim.y;
    uint offset = x + y * blockDim.x * gridDim.x; 

    float3 posf3 = posPtr[offset];//make_float3(43.5,55,0.66);//
    uint cellIndex = (uint)(posf3.z+1)*153*110 + (uint)(posf3.y)*153 + (uint)posf3.x;

    cache[threadIdx.x] = device_cons[cellIndex];
    __syncthreads();
    uint a = cache[threadIdx.x];
    a++;
    cache[threadIdx.x] = a;
    __syncthreads();

    device_cons[cellIndex] = cache[threadIdx.x]; 
}

推荐答案

使用推荐::排序，然后使用 thrust :: reduce_by_key 。但是，您还需要在排序后创建1的新向量（称为值）（并且与排序后的向量长度相同）。这些值将被相加以获得计数：

You can first sort the vector using thrust::sort and then use thrust::reduce_by_key. However, you also need to create a new vector (called values) of 1's (and of the same length as your sorted vector) after sort. These values will be added up to get the counts:

reduce_by_key is a generalization of reduce 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 
the keys_output. The corresponding values in the range are reduced using 
the plus and the result copied to values_output.

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