accumulate

Header

template<class InputIterator, class _TYPE> inline
_TYPE accumulate(InputIterator first, InputIterator last, _TYPE init)

template<class InputIterator, class _TYPE, class BinaryOperator> inline
_TYPE accumulate(InputIterator first, InputIterator last, _TYPE init, BinaryOperator binary_op)

accumulate repeatedly applies a function for each member of the input sequence, storing the result in a temporary storage.

The accumulate function initializes an accumulator acc with an initial value init and then modifies it with acc = acc + *i or acc = binary_op(acc,*i) for every iterator i in the range [first, last) in order. Normally, the accumulate function is used to sum the numeric elements of a vector. However, it can also be used to do other useful work such as concatenating a vector of strings.

Sample

// disable warning about symbols too long for debugger
#pragma warning (disable : 4786)

#include <iostream>
#include <numeric>
#include <functional>
#include <vector>
#include <iterator>
#include <string>

using namespace std;


typedef vector < float > FloatArray;
typedef vector < string > StringArray;
typedef ostream_iterator <float, char, char_traits <char> > FloatOstreamIt;

void main ()
{
    // a vector of floats
    FloatArray rgFA;

    // an ostream iterator that outputs a float to cout terminated
    // by a space
    FloatOstreamIt OstreamIt(cout," ");

    // Initialize the array to 1,1/2,1/3,...
    for (int i=0; i<10; i++) rgFA.push_back(1.0f/(i+1));

    // Print the array
    copy(rgFA.begin(),rgFA.end(),OstreamIt);
    cout << endl;

    // Sum the array
    cout << "The sum of 1 + 1/2 + 1/3 + ... + 1/10 is "
         << accumulate(rgFA.begin(),rgFA.end(),0.0f)
         << endl;

    // Compute the product of the array
    cout << "The product of 1 * 1/2 * 1/3 * ... * 1/10 is "
         << accumulate(rgFA.begin(),rgFA.end(),1.0f,multiplies<float>())
         << endl;

    // Initialize array of strings
    StringArray rgs;
    rgs.push_back("This ");
    rgs.push_back("is ");
    rgs.push_back("one ");
    rgs.push_back("sentence. ");

    // Concatenate the strings in the array and print the sentence
    cout << "The concatenated vector of strings: "
         << accumulate(rgs.begin(),rgs.end(),string(""))
         << endl;
}

Program Output

1 0.5 0.333333 0.25 0.2 0.166667 0.142857 0.125 0.111111 0.1
The sum of 1 + 1/2 + 1/3 + ... + 1/10 is 2.92897
The product of 1 * 1/2 * 1/3 * ... * 1/10 is 2.75573e-007
The concatenated vector of strings: This is one sentence.