Is there a “accummulate_if”?

Question

Is there a function similar to accummulate() but provides a unary pre-condition to filter the linear container when performing the operation? I search for

Answer 1

No, but you can write it yourself:

template
  <
  typename InputIterator,
  typename AccumulateType,
  typename BinaryOperation,
  typename Predicate
  >
const AccumulateType accumulate_if(
  InputIterator first,
  const InputIterator last,
  AccumulateType init,
  BinaryOperation&& binary_op,
  Predicate&& predicate)
{
  for (; first != last; ++first)
    if (predicate(*first)) init = binary_op(init, *first);
  return init;
}

Usage:

int main(int argc, char* argv[])
{
    std::vector v = {1,2,3,4,5};
    std::cout << accumulate_if(v.begin(), v.end(), 0, std::plus(), [] (int n) { return n > 3; });
    return 0;
} // outputs 9