Remove duplicate values from a vector<vector<string>>, not case sensitive? c++

Question

Hi i'm trying to remove duplicate values from my vector. It is set up as a vector. This vector contains a list of vectors, in each of the interior vectors is 3 strings.

I tried:

removeCopies.erase( unique(removeCopies.begin(), removeCopies.end() ), removeCopies.end());

but it still leaves some strings inside the interior vector like:

mainVector: {
interiorVector1: string 1: "book", string 2: "noun", string3: "A book"
interiorVector2: string 1: "book", string 2: "noun", string3: "a BOok"
}

I also can't just change it all to lowercase, I can't edit the values inside of the vector.

If you need a better explanation, please ask. Thank you.

edit:

I tried

unique(stringVec.begin(), stringVec.end(), [](const string &a, const string 
&b) { return lowercase(a) == lowercase(b); }), stringVec.end()

where lowercase() turns the entire string to lowercase. But it doesn't allow me to access the interior vector strings to do this.

AndyG · Accepted Answer · 2021-03-02 21:09:33Z

3

Just like std::sort, std::unique accepts a BinaryPredicate that in the case of unique is used for equals-comparison:

template< class ForwardIt, class BinaryPredicate >
constexpr ForwardIt unique( ForwardIt first, ForwardIt last, BinaryPredicate p );

If you provide a case-insensitive predicate, then it should work just fine. I recommend boost::iequals if you don't want to re-invent the wheel.

The following code won't work for your specific nested-vector example, but if you only had strings inside the vector the resultant code would look something like:

removeCopies.erase(std::unique(begin(removeCopies), end(removeCopies), boost::iequals), end(removeCopies));

In your case, you'll probably want to write a custom lambda that internally uses iequals to perform element-wise comparison.

Edit: Here is a discount-version of iequals:

bool iequals(const std::string& lhs, const std::string& rhs)
{
   if (lhs.size() != rhs.size())
      return false;
   for(size_t i = 0; i < lhs.size(); ++i)
   {
       if (std::tolower(lhs[i]) != std::tolower(rhs[i]))
          return false;
   }
   return true;
}

edited Mar 2, 2021 at 21:09

answered Mar 2, 2021 at 20:49

AndyG

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4 Comments

code1331 Over a year ago

ah I believe we are not allowed to use external libraries like boost.

AndyG Over a year ago

@code1331: It's fairly straightforward to write your own version of iequals. Use std::toupper (or std::tolower) to compare characters between strings.

code1331 Over a year ago

I tried string lowercase(string x) { transform(x.begin(), x.end(), x.begin(), [](char x) { return tolower(x); }); return x; } unique(stringVec.begin(), stringVec.end(), [](const string &a, const string &b) { return lowercase(a) == lowercase(b); } ), stringVec.end() sorry it wont let me format.

AndyG Over a year ago

@code1331 you don't need to declare a temporary string and use std::transform. You will get better performance with a regular loop that indexes into both the strings for comparison (and as a result will terminate after the minimum length). Inside the loop use std::tolower to get a lowercase version of each character in the respective strings. Then compare those characters for equivalance.

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