STL name for the "map" functional programming function

Vlion_26227 0
Viewed 26557

I would like to be able to write something like

char f(char);
vector<char> bar;
vector<char> foo = map(f, bar);

The transform function appears to be similar, but it will not autogenerate the size of the resultant collection.

map-function c++
5 Answers

You can mimic the map syntax above with something like

template<typename T, typename A>
T map(A(*f)(A), T & container) {
    T output;
    std::transform(container.begin(), container.end(), std::back_inserter(output), f);
    return output;
}
user_115477010

The std::transform function does the job, but isn't performant in some cases. I would suggest using a while loop and reserving the size before hand. This function can easily be changed to be used with strings or any thing mappable for that matter.

template<typename T, typename C>
std::vector<T> map(const std::vector<C> &array, auto iteratee) {
  int index = -1;
  int length = array.size();
  std::vector<T> v(length);
  while(++index < length) {
    v[index] = iteratee(array[index], index);
  }
  return v;
}

Calling the function where array is the std::vector you want to map.

auto result = map<int, int>(array, [](int elem, int index) {
  return elem + 10;
});

Running map on 100 000 000 with std::transform took ~6.15s

the while loop version took ~3.90s

user_76700900
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