stl----sort 与unique的调用次序和unique的用法

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <list>
using namespace std;

int main()
{
 
 int source[] = { 1, 4, 4, 6, 1, 2, 2, 3, 1, 6, 6, 6, 5, 7,
  5, 4, 4 };
 int sourceNum = sizeof(source)/sizeof(source[0]);

 vector<int> coll;

  
  copy (source, source+sourceNum,               //source
  back_inserter(coll)) ;                  //destination

  copy (coll.begin(), coll.end(), ostream_iterator<int>(cout," "));
  cout << "\n\n";

  sort(coll.begin(),coll.end());

 
 vector<int> :: iterator pos;
 pos = unique (coll.begin(), coll.end());
 copy (coll.begin(), coll.end(), ostream_iterator<int>(cout," "));
 cout << "\n\n";

 
 copy (coll.begin(), pos, ostream_iterator<int>(cout," "));     
 cout << "\n\n";

 
 copy (source, source+sourceNum,coll.begin());      

                 

 copy (coll.begin(), coll.end(),ostream_iterator<int>(cout," "));
 cout << "\n\n";

 //remove elements if there was a previous greater element
 coll.erase (unique (coll.begin(), coll.end(),greater<int>()), coll.end());
 
 copy (coll.begin(), coll.end(), ostream_iterator<int>(cout," "));
 cout << "\n\n";
}



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但是当要比较的数为计算所的的一个double，不能用sort和unique，怎么办？有没有好的办法啊！谢谢！

比如要比较的vector是从屏幕是得到的点的x坐标！坐标是通过鼠标时时得到！
要得到所有的不同的点的x坐标？

（可以用近似的算法）