C++/STL Algorithms Helper/accumulate

accumulate( ) computes a summation of all of the elements within a specified range and returns the result.

<source lang="cpp">

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

using namespace std;

int main() {

 vector<int> v(5);
 int i, total;
  
 for(i=0; i<5; i++) v[i] = i;
  
 total = accumulate(v.begin(), v.end(), 0);
  
 cout << total;
  
 return 0;

}

 </source>

accumulate value in a vector

<source lang="cpp">

1. include <numeric>
2. include <vector>
3. include <cmath>
4. include <iostream>

using namespace std; double arithmeticMean(const vector<int>& nums) {

 double sum = accumulate(nums.begin(), nums.end(), 0);
 return (sum / nums.size());

} int product(int num1, int num2) {

 return (num1 * num2);

} int main(int argc, char** argv) {

 vector<int> myVector;
 myVector.push_back(1);
 myVector.push_back(2);
 myVector.push_back(3);
 myVector.push_back(4);
 cout << "The arithmetic mean is " << arithmeticMean(myVector) << endl;
 return (0);

}

 </source>

Algorithm: Use accumulate to calculate product

<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 <vector>
3. include <deque>
4. include <list>
5. include <set>
6. include <map>
7. include <string>
8. include <algorithm>
9. include <iterator>
10. include <functional>
11. include <numeric>

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;

} /* INSERT_ELEMENTS (collection, first, last)

* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/

template <class T> inline void INSERT_ELEMENTS (T& coll, int first, int last) {

   for (int i=first; i<=last; ++i) {
       coll.insert(coll.end(),i);
   }

}

int main() {

   vector<int> coll;
   INSERT_ELEMENTS(coll,1,9);
   PRINT_ELEMENTS(coll);

   // process product of elements
   cout << "product: "
        << accumulate (coll.begin(), coll.end(),    // range
                       1,                           // initial value
                       multiplies<int>())           // operation
        << endl;
   // process product of elements (use 0 as initial value)
   cout << "product: "
        << accumulate (coll.begin(), coll.end(),    // range
                       0,                           // initial value
                       multiplies<int>())           // operation
        << endl;

} /* 1 2 3 4 5 6 7 8 9 product: 362880 product: 0

*/        
   
 </source>

Calculate sum of elements in a vector

<source lang="cpp">

1. include <iostream>

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

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

int main() {

  std::ostream_iterator< int > output( cout, " " );
  int a2[ 10 ] = { 100, 2, 8, 1, 50, 3, 8, 8, 9, 10 };
  std::vector< int > v2( a2, a2 + 10 ); // copy of a2
  cout << "\n\nVector v2 contains: ";
  std::copy( v2.begin(), v2.end(), output );
  // calculate sum of elements in v
  cout << "\n\nThe total of the elements in Vector v is: "
     << std::accumulate( v2.begin(), v2.end(), 0 );
  cout << endl;
  return 0;

} /*

Vector v2 contains: 100 2 8 1 50 3 8 8 9 10 The total of the elements in Vector v is: 199

*/        
   
 </source>

Compute the mean float mean with accumulate function

<source lang="cpp">

1. include <algorithm>
2. include <cmath>
3. include <functional>
4. include <iostream>
5. include <list>
6. include <numeric>
7. include <vector>

using namespace std; template <class T> void print(T& c){

  for( typename T::iterator i = c.begin(); i != c.end(); i++ ){
     std::cout << *i << endl;
  }

} int main( ) {

  const float a[] = { 1, 1.3, 1.5, 0.9, 0.1, 0.2};
  // create and initialize vector with above data
  vector<float> data( a,a + sizeof( a ) / sizeof( a[0] ) );
  cout << "DATA VECTOR HAS " << data.size() << " ELEMENTS\n";
  print( data  );
  // compute the mean
  float mean = accumulate( data.begin(), data.end(), 0.0f )/ data.size();

}

 </source>

Demonstrating the generic accumulate algorithm with a reverse iterator

<source lang="cpp">

1. include <iostream>
2. include <vector>
3. include <cassert>
4. include <numeric> // For accumulate

using namespace std; int main() {

 float small = (float)1.0/(1 << 26);
 float x[5] = {1.0, 3*small, 2*small, small, small};
 
 vector<float> vector1(&x[0], &x[5]); 
 cout << "Values to be added: " << endl;
 vector<float>::iterator i;
 cout.precision(10);
 for (i = vector1.begin(); i != vector1.end(); ++i)
   cout << *i << endl;
 cout << endl;
 float sum1 = accumulate(vector1.rbegin(), vector1.rend(),(float)0.0);
 cout << "Sum accumulated from right = " << (double)sum1 << endl;
 return 0;

} /* Values to be added: 1 4.470348358e-008 2.980232239e-008 1.490116119e-008 1.490116119e-008 Sum accumulated from right = 1.000000119

*/        
   
 </source>

Finding the Mean Value

<source lang="cpp">

1. include <iomanip>
2. include <iostream>
3. include <numeric>
4. include <vector>

using namespace std; int main( ) {

  // miles per gallon for different cars in fleet
  const float mpg_data[] = { 1.1, 9.9, 8.8, 3.3, 2.2, 2.2,4.4 };
  // create a vector and initialize it with the above data
  vector<float> mpg( mpg_data,mpg_data + sizeof( mpg_data ) / sizeof( mpg_data[0] ) );
  // mean
  float fleet_average = accumulate( mpg.begin(), mpg.end(), 0.0 )/ mpg.size();
  cout << fleet_average << endl;

}

 </source>

Illustrating the generic accumulate algorithm with predicate

<source lang="cpp">

1. include <iostream>
2. include <cassert>
3. include <algorithm>
4. include <functional>
5. include <numeric>

using namespace std; int main() {

 int x[20];
 
 for (int i = 0; i < 20; ++i)
   x[i] = i;
// Show that 10 * 1 * 2 * 3 * 4 == 240:
 int result = accumulate(&x[1], &x[5], 10, multiplies<int>());
 cout << result;

 
 return 0;

} /* 240

*/        
   
 </source>

Use accumulate() and minus()

<source lang="cpp">

1. include <iostream>
2. include <numeric>

using namespace std; int main() {

  double v1[3] = {1.0, 2.2, 4.3}, sum;
  sum = accumulate(v1, v1 + 3, 0.0, minus<int>());
  cout << "sum = " << sum << endl;

}

 </source>

Use accumulate to calculate sum for double array with minus()

<source lang="cpp">

1. include <iostream>
2. include <numeric>

using namespace std; int main() {

  double v1[3] = {1.0, 2.2, 4.3}, sum;
  sum = accumulate(v1, v1 + 3, 0.0, minus<int>());
  cout << "sum = " << sum << endl;

}

 </source>