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

Copy elements from vector to another vector, removing elements greater than 9 (remove_copy_if)

<source lang="cpp">#include <iostream>

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

using namespace std; bool greater9( int ); int main() {

  const int SIZE = 10;
  int a[ SIZE ] = { 10, 2, 10, 4, 16, 6, 14, 8, 12, 10 };
  // Remove 10 from v
  vector< int > v( a, a + SIZE );
  vector< int >::iterator newLastElement;
  newLastElement = remove( v.begin(), v.end(), 10 );
  // Copy elements from v4 to c, removing elements greater than 9
  vector< int > v4( a, a + SIZE );
  vector< int > c2( SIZE, 0 );
  remove_copy_if( v4.begin(), v4.end(), c2.begin(), greater9 );
  cout << endl;
  return 0;

} bool greater9( int x ) {

  return x > 9;

}</source>

Remove all odd numbers from the vector using remove_if

<source lang="cpp">#include <algorithm>

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

using namespace std; template <typename elementType> bool IsOdd (const elementType& number){

   return ((number % 2) == 1);

} int main (){

   list <int> l;
   for (int nCount = 0; nCount < 10; ++ nCount)
       l.push_back (nCount);
   list <int>::const_iterator li;
   for ( li = l.begin (); li != l.end (); ++ li )
       cout << *li << " ";
   vector <int> v (l.size () * 2);
   vector <int>::iterator iLastPos;
   iLastPos = copy ( l.begin (), l.end (), v.begin () );
   vector <int>::iterator i;
   i = remove_if (v.begin (), v.end (), IsOdd <int>);    // The predicate
   v.erase (i , v.end ());
   vector <int>::iterator vi;
   for ( vi = v.begin (); vi != v.end (); ++ vi )
       cout << *vi << " ";
   return 0;

}</source>

removeif, bind2nd() and list

<source lang="cpp">#include <iostream>

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

using namespace std;

int main() {

 list<int> list1;
 list<int>::iterator p, endp;
  
 int i;
  
 for(i=1; i < 20; i++) list1.push_back(i);
  
 p = list1.begin();
 while(p != list1.end()) {
   cout << *p << endl;
   p++;
 }
 endp = remove_if(list1.begin(), list1.end(),bind2nd(greater<int>(), 4));
  
 p = list1.begin();
 while(p != endp) {
   cout << *p << endl;
   p++;
 }
 return 0;

}</source>

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: ");

}</source>

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

Remove value from vector with condition with remove_if()

<source lang="cpp">#include <iostream>

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

using namespace std; bool greater9( int ); int main() {

  const int SIZE = 10;
  int a[ SIZE ] = { 10, 2, 10, 4, 16, 6, 14, 8, 12, 10 };
  // Remove 10 from v
  vector< int > v( a, a + SIZE );
  vector< int >::iterator newLastElement;
  newLastElement = remove( v.begin(), v.end(), 10 );
  // Remove elements greater than 9 from v3
  vector< int > v3( a, a + SIZE );
  newLastElement = remove_if( v3.begin(), v3.end(), greater9 );
  return 0;

} bool greater9( int x ) {

  return x > 9;

}</source>

Use predicate in std::remove_if

<source lang="cpp">#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;

}</source>

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

Use remove_if() to remove all elements from list that are greater than 10.

<source lang="cpp">#include <iostream>

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

using namespace std; int main() {

 list<int> list1;
 list<int>::iterator res_itr;
 for(unsigned i=1; i < 20; ++i) list1.push_back(i);
 res_itr = remove_if(list1.begin(), list1.end(),bind2nd(greater<int>(), 10));
 return 0;

}</source>