CODEWITHSUNDEEP
c++vectorbooleanstdvector
clicking games
clicking games

Reputation: 5

How to sort all members with a value of false to the end of a vector?

I want to sort a vector of bools by their value. This is the list:

std::vector<bool> bolis {true true false true false false true true};

Is there some kind of function that would make this list equal to this:

{true,true,true,true,true,false,false,false}

I saw the std::sort function but it seems the only real use of it is to sort a list of ints or floats and not a list of bools.

Upvotes: 0

Views: 390

Answers (3)

jignatius
jignatius

Reputation: 6494

The std::partition function from the standard library is designed for doing exactly what you want to do. It accepts a range and a predicate, and reorders the elements of the range so that they are partitioned according to this predicate:

#include <iostream>
#include <vector>
#include <iterator>
#include <algorithm>


int main()
{
    std::vector<bool> bolis {true, true, false, true, false, false, true, true};

    //reorder so that true comes first    
    std::partition(bolis.begin(), bolis.end(), [](bool b){return b;});

    std::cout << std::boolalpha;
    std::copy(bolis.begin(), bolis.end(), std::ostream_iterator<bool>(std::cout, " " ));
    
    return 0;    
}

Output:

true true true true true false false false

Here's a demo.

Upvotes: 0

Deepak Tatyaji Ahire
Deepak Tatyaji Ahire

Reputation: 5311

First Method:

This can be achieved by defining the custom comparator function and passing it to the sort function.

Have a look at the implementation as follows:

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



//define the function:
bool comparator(bool lhs, bool rhs) { return rhs < lhs; }

int main()
{
    std::vector<bool> bolis {true, true, false, true, false, false, true, true};
    
    // pass it to sort:
    sort(bolis.begin(), bolis.end(), &comparator);
    
    for(int i=0;i<bolis.size();i++){
        std::cout<<(bolis[i] ? "true " : "false ");
    }
    std::cout<<std::endl;
}

Output:

true true true true true false false false

Second method in O(N) time complexity:

Count the number of true and false values in the vector and print them accordingly.

For example, if there are 5 true values and 2 false values, then print true for 5 number of number of times and false for 2 number of times.

Or you can push the values in another vector as well or edit the original vector.

Thanks to @john for all the suggestions to improve the answer!

Upvotes: 1

Scheff&#39;s Cat
Scheff&#39;s Cat

Reputation: 20141

To sort a std::vector<bool> is a very specific case, and can be done by a very specific solution:

counting the number of true elements and then rewrite the vector based on this count.

Sample code:

#include <vector>
#include <iostream>

int main()
{
  std::vector<bool> bolis {true, true, false, true, false, false, true, true};
  // count number of true
  size_t nT = 0;
  for (bool value : bolis) nT += value == true;
  // write sorted vector
  for (size_t i = 0, n = bolis.size(); i < n; ++i) bolis[i] = i < nT;
  // show result
  const char *sep = "";
  for (bool value : bolis) {
    std::cout << sep << std::boolalpha << value;
    sep = ", ";
  }
}

Output:

true, true, true, true, true, false, false, false

Live Demo on coliru

Upvotes: 1

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