How can I avoid "for" loops with an "if" condition inside them with C++?

Question

With almost all code I write, I am often dealing with set reduction problems on collections that ultimately end up with naive "if" conditions inside of them. Here's a simple example:

for(int i=0; i<myCollection.size(); i++) {      if (myCollection[i] == SOMETHING)      {            DoStuff();      } } 

With functional languages, I can solve the problem by reducing the collection to another collection (easily) and then perform all operations on my reduced set. In pseudocode:

newCollection <- myCollection where <x=true map DoStuff newCollection 

And in other C variants, like C#, I could reduce with a where clause like

foreach (var x in myCollection.Where(c=> c == SOMETHING))  {    DoStuff(); } 

Or better (at least to my eyes)

myCollection.Where(c=>c == Something).ToList().ForEach(d=> DoStuff(d)); 

Admittedly, I am doing a lot of paradigm mixing and subjective/opinion based style, but I can't help but feel that I am missing something really fundamental that could allow me to use this preferred technique with C++. Could someone enlighten me?

Answer 1

IMHO it's more straight forward and more readable to use a for loop with an if inside it. However, if this is annoying for you, you could use a for_each_if like the one below:

template<typename Iter, typename Pred, typename Op>  void for_each_if(Iter first, Iter last, Pred p, Op op) {   while(first != last) {     if (p(*first)) op(*first);     ++first;   } } 

Usecase:

std::vector<int> v {10, 2, 10, 3}; for_each_if(v.begin(), v.end(), [](int i){ return i > 5; }, [](int &i){ ++i; }); 

Live Demo