The STL algorithms offer a powerful way to solve some base programming use cases. If you know and use these algorithms you can write more clean, efficient and robust code. But unfortunately, it isn’t that easy to know or find the right algorithm for a use case. In my opinion, this is a result of the not practical kind of documentation – especially grouping of the algorithms is not related to practice – and on the other hand the unfavorable naming of some functions. Therefore, I write this series of articles and want to give a more practice-related overview about the STL algorithms.

Within this article I want to give an overview about the STL algorithms to change and sort container elements. This is one of a series of articles. Within each of these blog post I want to summarize the STL algorithms regarding one kind of use case.

Each section contains a list of the according STL algorithms with a short description. Additional you will find an example implementation which will show some of these algorithms. If you copy and execute the examples, you will see the results within the console window. Additional, you will see the results as comment within the source code.

Most of the standard algorithms take half-open sequences. “Half-open” means the start iterator refers to the first element of the sequence and the end iterator refers to the element behind the last element. Returning the end iterator of the sequence to indicate “not found” is a standard-library convention.

Change container elements

void Print(const std::vector& data)
{
  std::for_each(data.begin(), data.end(), [](int element){ std::cout << element << " "; });
  std::cout << std::endl;
}

int _tmain(int argc, _TCHAR* argv[])
{
  std::vector data{ 5, 7, 9, 2, 4};

  // replace if
  std::replace_if(data.begin(), data.end(), [](int element){return element < 7; }, 0);
  Print(data);    // output is '0 7 9 0 0'

  // transform
  std::transform(data.begin(), data.end(), data.begin(), [](int element) {return element + 20; });
  Print(data);    // output is '20 27 29 20 20'

  return 0;
}

Sort container elements

void Print(const std::vector& data)
{
  std::for_each(data.begin(), data.end(), [](int element){ std::cout << element << " "; });
  std::cout << std::endl;
}

int _tmain(int argc, _TCHAR* argv[])
{
  std::vector data{ 5, 7, 9, 2, 4};

  // sort
  std::sort(data.begin(), data.end());
  Print(data);    // output is '2 4 5 7 9'
    
  // partial sort
  data = { 5, 7, 9, 2, 4 };  
  std::partial_sort(data.begin(), data.begin()+2, data.end());
  Print(data);    // output is '2 4 9 7 5'

  // rotate to right
  data = { 5, 7, 9, 2, 4 };
  std::rotate(data.rbegin(), data.rbegin() + 1, data.rend());
  Print(data);    // output is '4 5 7 9 2'

  // partition
  data = { 5, 7, 9, 2, 4 };
  std::partition(data.begin(), data.end(), [](int element){return element > 6; });
  Print(data);    // output is '9 7 5 2 4'

  // stable partition
  data = { 5, 7, 9, 2, 4 };
  std::stable_partition(data.begin(), data.end(), [](int element){return element > 6; });
  Print(data);    // output is '7 9 5 2 4'

  // shuffle
  data = { 5, 7, 9, 2, 4 };
  std::random_device randomDevice;
  std::mt19937 randomNumberGenerator(randomDevice());
  std::shuffle(data.begin(), data.end(), randomNumberGenerator);
  Print(data);    // output is different on each execution

  return 0;
}