Question: Is it possible to sort objects using the Thrust library?
I have the following struct:

```
struct OB{
  int N;
  Cls *C; //CLS is another struct.
}

```

Is it possible to use thrust in order to sort an array of OB according to N? Can you provide a simple example on using thrust to sort objects? If thrust is not able to do so, is there any other CUDA libraries that allows me to do so?

Answer: 
you can sort objects by overloading operator< . For example:

```
__host__ __device__ struct Color{
  double blue, green, red;
  double distance;
  void dist()
  {
    distance = sqrt(blue*blue + green*green + red*red);
  }
};

__host__ __device__ bool operator<(const Color &lhs, const Color &rhs) 
{
   return lhs.distance < rhs.distance;
}

int main(void)
{
   thrust::device_vector<Color> cd;
   thrust::host_vector<Color> ch;
   for (int i = 0; i<6; i++)
   {
      Color c;
      c.blue = rand()*255;
      c.green = rand()*255;
      c.red = rand()*255;
      c.dist();
      ch.push_back(c);
   }
   cd = ch;
   thrust::sort(cd.begin(), cd.end());
   ch = cd;
   return 0;
}

```

the objects will be sorted after the distance.
I have not tried **Thrust** yet, but there is a similar sort function in [CUDPP](http://code.google.com/p/cudpp/) called **cudppSort**. You cannot directly sort structures using cudppSort, it can only handle integers or floats.

So, one way to sort array of structures is to sort the keys (of your structure) and an index array of values along with it. Later, use the sorted index array to move the structures to their final sorted locations. I have described how to do this for the cudppCompact compaction algorithm in a blog post [here](http://choorucode.wordpress.com/2011/03/09/cudpp-compacting-a-structure-array/). The technique should be similar for cudppSort too.