How to sort a vector of strings in a specific predetermined order?

Question

The problem: I need to sort a vector of strings in exact specific order. Let say we have a constant vector or a array with the exact order:

vector<string> correctOrder = {"Item3", "Item1", "Item5", "Item4", "Item2"};

Next, we have a dynamic incoming vector which will have same Items, but they maybe mixed and less in number.

vector<string> incommingVector = {"Item1", "Item5", "Item3"};

So I need to sort the incomming vector with the order like the first vector, correctOrder, and the result must be:

vector<string> sortedVector = {"Item3", "Item1", "Item5"};

I think the correct order may be represented in a different way, but can't figure out. Can someone help me please?

Answer 1

If the default comparison is not enough (lexicographic comparison) then the simplest thing you can do is to provide the sort function with a lambda that tells it which string come first. You can have a unordered_map<string,int> with the strings in your correctorder vector as keys and their corresponding position in the sorted array as values.

The cmp function will simply compare the values of the keys you provide in your incommingVector.

unordered_map<string, int> my_map;
for(int i = 0 ; i < correctorder.size() ; i++)
   my_map[correctorder[i]]=i;

auto cmp =[&my_map](const string& s, const string& s1){
   return my_map[s] < my_map[s1];
}   

sort(incommingVector.begin(), incommingVector.end() , cmp);