Erasing case in-sensitive duplicates from std::vector<std::string>

Question

This is weird, can't erase remove case in-sensitive duplicates from std::vector? Can someone please let me know how to achieve this? Here is my code:

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>

using namespace std;

int main()
{
    vector<string> stringVec = {"John", "Bob", "Joe", "Zack", "Randy", "bob", "joe", "andy"};
    sort(stringVec.begin(), stringVec.end());
    stringVec.erase(unique(stringVec.begin(), stringVec.end()),stringVec.end());

    for(unsigned i=0; i<stringVec.size(); i++)
    {
        cout<<stringVec[i]<<endl;
    }

    return 0;
}

Output for above code:

Success time: 0 memory: 3432 signal:0
Bob
Joe
John
Randy
Zack
andy
bob
joe

I expect at least joe, bob to be removed and andy to be placed in first index.

Answer 1

You can solve this by passing a case-insensitive predicate to both sort() and unique():

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>

using namespace std;

string lowercase(string x)
{
  transform(x.begin(), x.end(), x.begin(), [](char x) { return tolower(x); });
  return x;
}


int main()
{
    vector<string> stringVec = {"John", "Bob", "Joe", "Zack", "Randy", "bob", "joe", "andy"};
    sort(stringVec.begin(), stringVec.end(),
      [](const string &a, const string &b) { return lowercase(a) < lowercase(b); }
    );
    stringVec.erase(
      unique(stringVec.begin(), stringVec.end(),
        [](const string &a, const string &b) { return lowercase(a) == lowercase(b); }
      ),
      stringVec.end()
    );

    for(unsigned i=0; i<stringVec.size(); i++)
    {
        cout<<stringVec[i]<<endl;
    }

    return 0;
}

Live example