C++/STL Algorithms Modifying sequence operations/remove if

remove_if for list

<source lang="cpp">

/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <list>
3. include <algorithm>

using namespace std; /* PRINT_ELEMENTS()

* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/

template <class T> inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="") {

   typename T::const_iterator pos;
   std::cout << optcstr;
   for (pos=coll.begin(); pos!=coll.end(); ++pos) {
       std::cout << *pos << " ";
   }
   std::cout << std::endl;

}

class Nth { // function object that returns true for the nth call

 private:
   int nth;       // call for which to return true
   int count;     // call counter
 public:
   Nth (int n) : nth(n), count(0) {
   }
   bool operator() (int) {
       return ++count == nth;
   }

}; int main() {

   list<int> coll;
   // insert elements from 1 to 9
   for (int i=1; i<=9; ++i) {
       coll.push_back(i);
   }
   PRINT_ELEMENTS(coll,"coll:        ");
   // remove third element
   list<int>::iterator pos;
   pos = remove_if(coll.begin(),coll.end(),  // range
                   Nth(3));                  // remove criterion
   coll.erase(pos,coll.end());
   PRINT_ELEMENTS(coll,"nth removed: ");

}

/* 

coll: 1 2 3 4 5 6 7 8 9 nth removed: 1 2 4 5 7 8 9

*/       
   
 </source>

Removing All Matching Elements

<source lang="cpp">

1. include <algorithm>
2. include <functional>
3. include <iostream>
4. include <iterator>
5. include <numeric>
6. include <vector>

using namespace std; int main( ) {

  const int last_number = 50;
  vector<int> v( last_number - 1, 1 );
  v[0] = 2;
  partial_sum( v.begin(), v.end(), v.begin() );
  vector<int>::iterator stop = v.end();
  for( vector<int>::iterator start = v.begin(); start != stop;++start )
  // remove all subsequent numbers that are not divisible by the current one
  stop = remove_if( start+1, stop,not1( bind2nd( modulus<int>(), *start ) ) );
  cout << "Prime numbers: ";
  copy( v.begin(), stop, ostream_iterator<int>( cout, " " ) );

}

 </source>

Use predicate in std::remove_if

<source lang="cpp">

1. include <iostream>

using std::cout; using std::endl;

1. include <algorithm>
2. include <vector>
3. include <iterator>

bool greater9( int ); int main() {

  int a[ 10 ] = { 10, 2, 10, 4, 16, 6, 14, 8, 12, 10 };
  std::ostream_iterator< int > output( cout, " " );
  std::vector< int > v3( a, a + 10 ); // copy of a
  cout << "Vector v3 before removing all elements"
       << "\ngreater than 9:\n   ";
  std::copy( v3.begin(), v3.end(), output );
  // remove elements greater than 9 from v3
  std::vector< int >::iterator newLastElement = std::remove_if( v3.begin(), v3.end(), greater9 );
  cout << "\nVector v3 after removing all elements"
     << "\ngreater than 9:\n   ";
  std::copy( v3.begin(), newLastElement, output );
  return 0;

} bool greater9( int x ) {

  return x > 9;

} /* Vector v3 before removing all elements greater than 9:

  10 2 10 4 16 6 14 8 12 10

Vector v3 after removing all elements greater than 9:

  2 4 6 8 
*/
       
   
 </source>