how can I find repeated elements in a vector [duplicate] - c++

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This question already has answers here:
Checking for duplicates in a vector [duplicate]
(5 answers)
Closed 9 years ago.
I have a vector of int which can include maximum 4 elements and minimum 2, for example :
std::vector<int> vectorDATA(X); // x means unknown here
What I want to do is to erase the elements that are repeated for example :
vectorDATA{1,2,2} to vectorDATA{1,2}
vectorDATA{1,2,3} to nothing changes
vectorDATA{2,2,2} to vectorDATA{2}
vectorDATA{3,2,1,3} to vectorDATA{3,2,1}
vectorDATA{1,2,1,2} to vector{1,2}
and so on
here a code simple :
cv::HoughLines(canny,lineQ,1,CV_PI/180,200);
std::cout << " line Size "<<lineQ.size()<< std::endl;
std::vector<int> linesData(lineQ.size());
std::vector<int> ::iterator it;
if(lineQ.size() <=4 && lineQ.size() !=0 ){
if(lineQ.size()==1){
break;
}else {
for ( int i = 0; i<lineQ.size();i++){
linesData[i] = lineQ[i][1]; // my comparison parameter is the lineQ[i][1]
}
// based on the answer I got I'm trying this but I really don't how to continue ?
std::sort(lineQ.begin(),lineQ.end(),[](const cv::Vec2f &a,const cv::Vec2f &b)
{
return ????
}
I tried use a for and do while loop, but I didn't get it, and the function std::adjacent_find this has a condition that the elements should be consecutive.
Maybe it's easy but I just don't get it !
thanks for any help !

Answer 1

The easy way is sort then unique-erase, but this changes order.
The c++11 order preserving way is to create an unordered_set<int> s; and do:
unordered_set<int> s;
vec.erase(
std::remove_if( vec.begin(),vec.end(), // remove from vector
[&](int x)->bool{
return !std::get<1>(s.insert(x)); // true iff the item was already in the set
}
),
vec.end() // erase from the end of kept elements to the end of the `vec`
);
which is the remove-erase idiom using the unordered_set to detect duplicates.

Answer 2

I didn't see a sort-less source code in the already mentioned answers, so here it goes. Hash table for checking duplicates, shifting unique elements towards the front of the vector, note that src is always >= dst and dst is the number of copied, i.e. unique elements at the end.
#include <unordered_set>
#include <vector>
#include <iostream>
void
uniq (std::vector<int> &a) {
std::unordered_set<int> s;
size_t dst = 0;
for (size_t src = 0; src < a.size(); ++src) {
if (s.count (a[src]) == 0) {
s.insert (a[src]);
a[dst++] = a[src];
}
}
a.resize (dst);
}
int
main () {
std::vector<int> a = { 3, 2, 1, 3, 2, 1, 2, 3, 4, 5 ,2, 3, 1, 1 };
uniq (a);
for (auto v : a)
std::cout<< v << " ";
std::cout << std::endl;
}

Answer 3

If you want to realy remove repeated elements, you may try something like this:
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main () {
int data[] = {1,2,3,2,1};
vector<int> vectorDATA = (&data[0], &data[0] + 5);
sort(vectorDATA.begin(),vectorDATA.end());
for(int i = 0; i < vectorDATA.size()-1; ++i)
{
if(vectorDATA[i] == vectorDATA[i+1])
vectorDATA.erase(vectorDATA.begin()+i+1);
}
for(int i = 0; i < vectorDATA.size();++i)
{
cout << vectorDATA[i] << " ";
}
cout << endl;
return 0;
}
Lack of of this method is then elements lost his order.