Remove duplicate strings in string vector

Question

I have the code, listed below, which I am trying to get to remove any duplicate football team names from a string vector. However, it is only working sometimes, it will remove duplicate names for some of the teams; but then for others there will be multiple occurrences of the same team name in the final array.

For example it would print:

aresnal
wigan
villa
liverpool
villa

Notice there are two 'villa' names, could anyone give me a suggestion? The 'finalLeague' is the array which is storing all of the names, and is the array which needs the duplicates removing out of.

  for (int i = 0;i < finalLeague.size();i++)
  {       
      string temp = finalLeague[i];
      int h = i + 1;
      for (int j = i+1;j < finalLeague.size();j++)
      {
          if (finalLeague[j] == finalLeague[i])
          {               
              finalLeague.erase(finalLeague.begin()+j);     
          }     
      }
  }

it will be easy to check when you add an element : if the element already exist don't add it . — unfamous
– unfamous, Commented Dec 17, 2013 at 13:57

juanchopanza · Accepted Answer · 2013-12-17 13:28:38Z

7

Sure, you can use a combination of std::sort, std::unique and std::vector::erase:

std::sort(finalLeague.begin(), finalLeague.end());
auto it = std::unique(finalLeague.begin(), finalLeague.end());
finalLeague.erase(it, finalLeague.end());

Alternatively, use a container that does not accept duplicates in the first place:

std::set<std::string> finalLeague;           // BST, C++03 and C++11
std::unordered_set<std::string> finalLeague; // hash table, C++11

edited Dec 17, 2013 at 13:28

answered Dec 17, 2013 at 12:58

juanchopanza

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Comments

Ranveer · Accepted Answer · 2013-12-17 13:09:30Z

0

This can also be done using a hashmap. Using #include <unordered_map> will let you use it. Note that you might have to use C++ 11 for it. Read about unordered maps here.

All you need to do is check whether the string has occurred before or not and keep pushing unique strings into a new vector.

USP of this method is that it needs minimal amount of code. Just one loop would do the trick.

edited Dec 17, 2013 at 13:09

answered Dec 17, 2013 at 13:04

Ranveer

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4 Comments

luk32 Over a year ago

It not available since c++11. It's officially standardized since c++11. It is available in many popular c++ compilers as an extension since long ago.

luk32 Over a year ago

In gcc it was present already in 3.4 as hash_map. There is a bugfix report in change log. And this dates back to 2006. I believe that vc++ had something similar. But of course there might be differences, although my point is simply if one has and old pre-c++11 compiler, they should not get discouraged in case they need similar functionality.

Pete Becker Over a year ago

std::map will also work. It's the map part that matters initially, not the implementation detail.

Ranveer Over a year ago

I guess my answer should have been just that he could also use hashmaps.

Jepessen · Accepted Answer · 2013-12-17 13:17:27Z

0

you should use std::unique

std::vector<std::string> vec;
// filling vector
// ....

std::vector<std::string>::iterator it;
it = std::unique (vec.begin(), vec.end());
vec.resize(std::distance(vec.begin(),it));

@edit: as @Gorpik said, vector must be sorted before use std::unique, otherwise only equal consecutive elements will be deleted.

edited Dec 17, 2013 at 13:17

answered Dec 17, 2013 at 13:03

Jepessen

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1 Comment

Gorpik Over a year ago

std::unique only removes consecutive duplicates. You would need to sort the vector before using it.

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