(C++) std::partition

January 9, 2018 · View on GitHub

 

 

 

 

 

(C++) std::partition

 

std::partition is an STL algorithm to partition elements in a container by a certain predicate. For example, in the code shown below, a std::vector is partitioned into primes and non-primes. Note that the order of the non-primes has changed. If the ordering must remain, use std::stable_partition.

 

 

#include <algorithm> #include <cassert> #include <cmath> #include <iostream> #include <iterator> #include <vector> //From http://www.richelbilderbeek.nl/CppIsPrime.htm bool IsPrime(const int x) {   const int max   = static_cast<int>(       std::sqrt(static_cast<double>(x))     ) + 1;   for (int i=2; i!=max; ++i)   {     if (x % i == 0) return false;   }   return true; } int main() {   std::vector<int> v;   for (int i=1; i!=10; ++i) v.push_back(i);   //Partition the std::vector in primes and non-primes   typedef std::vector<int>::iterator Iterator;   const Iterator p_end = std::partition(v.begin(),v.end(),IsPrime);   std::cout << "Primes: ";   std::copy(v.begin(),p_end,std::ostream_iterator<int>(std::cout," "));   std::cout << "\nNon-primes: ";   std::copy(p_end,v.end(),std::ostream_iterator<int>(std::cout," ")); }

 

Screen output:

 

Primes: 1 2 3 7 5 Non-primes: 6 4 8 9