How to remove duplicates from std::vector >

Question

how to remove duplicate values from

std::vector <std::pair<UnicodeString, UnicodeString> > myVect;

Is there any built in function or i need to write a custom code for this

unique() removes adjacent duplicates, so you can sort your vector and then do a unique(). — DumbCoder, Mar 22 '11 at 11:51
If you wish to only have unique values in your container, consider using std::set. — johnsyweb, Mar 22 '11 at 11:54
Take a look at similar question http://stackoverflow.com/questions/1041620/most-efficient-way-to-erase-duplicates-and-sort-a-c-vector — Oleg Svechkarenko, Mar 22 '11 at 12:03

score 6 · Accepted Answer · edited May 23 '17 at 12:04

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Assuming that (a) a std::set is not what you want [that is you want to allow duplicate elements in your std::vector, only to remove them later] and (b) you don't wish to change the order of the elements in your std::vector [that is, the current order is important], which are both reasonable situations... You should be able to adapt Fred Nurk's answer to How can I remove duplicate values from a list in C++ buy substituting vector for list and modifying the less comparators accordingly.

edited May 23 '17 at 12:04

Community

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answered Mar 22 '11 at 12:00

johnsyweb

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But, if he uses Fred's answer with `vector`, won't he get O(N^2) behavior, since `vector::erase()` is O(N) while `list::erase()` is O(1)? Is there a solution that works well with vectors? – Robᵩ Mar 22 '11 at 15:24
@Rob: Good point. Since, I don't know (a) whether `std::set` is acceptable, (b) whether @jame can `sort` the vector or (c) whether speed is an issue, I'll leave my answer as-is for now. – johnsyweb Mar 22 '11 at 20:39

score 2 · Answer 2 · answered Mar 22 '11 at 13:43

The best way to do it, if you can modify the order in your vector is the following:

   std::sort(myVect.begin(), myVect.end());
   myVect.erase(std::unique(myVect.begin(), myVect.end()), myVect.end());

Just make sure UnicodeString accepts the < operator.

However, you may want to use a different structure such as std::set or std::unordered_set to have an unique guarantee at insertion.

How to remove duplicates from std::vector >

2 Answers2