How do I sort a vector with respect to another vector?

Question

I have few vectors with same data type as.

   v  < int > = {5,4,1,2}
   v2 < int > = {2,4,3,5,1,6,8,7}
   v3 < int > = {1,4,2,3}

There is any way to sort vector v2 , v3 ... with respect to vector v using STL of C++(algorithm) so that

after sorting v2 would be {5,4,1,2,3,6,7,8} when it's sorted with respect to v and v3 would be {4,1,2,3} when it's sorted with respect to v .

Edit:

It may be unclear for some people. let me explain ..
sorted vector has two parts , one is A and another one is B .
A contains element of vector v i.e. A is subset of v ,it follows same order as it's in v
B contains remaining element{v_i - A} of given vector(v_i) and it's sorted .
so for vector v2 after sorting it would be

 v2 = A union B
 A = {5,4,1,2}
 B = {3,6,7,8}

It's not entirely clear (at least to me) exactly what you're trying to accomplish here. What do you mean by sorting A with respect to B (for whatever values of A and B)? — Jerry Coffin, Sep 24 '14 at 19:52
check it it's there . http://www.cplusplus.com/reference/algorithm/ — user3919801, Sep 24 '14 at 19:52
@user3919801 that would be [`algorithm`](http://en.cppreference.com/w/cpp/algorithm), not `algorithm.h`. And your description is still clear as an autumn London fog. — WhozCraig, Sep 24 '14 at 21:20

Igor Tandetnik · Accepted Answer · 2014-09-24T20:44:44.780

1

class StrangeComparison {
public:
  StrangeComparison(const vector<int>& ordering) : ordering_(ordering) {}
  bool operator()(int a, int b) const {
    auto index_a = find(ordering_.begin(), ordering_.end(), a);
    auto index_b = find(ordering_.begin(), ordering_.end(), b);
    return make_pair(index_a, a) < make_pair(index_b, b);
  }
private:
  const vector<int>& ordering_;
};

sort(v2.begin(), v2.end(), StrangeComparison(v));

Working example. Improving efficiency is left as an exercise for the reader (hint: look at std::find calls).

edited Sep 24 '14 at 20:44

answered Sep 24 '14 at 20:30

Igor Tandetnik

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It's not working in old compiler less than C++ 11. i.e. it's working in C++ 11 . check out here http://ideone.com/HjU0u8 i tried by changing auto to int , still not working .. – user3919801 Sep 25 '14 at 12:10
1

It shouldn't be `int` - make it `vector::const_iterator` – Igor Tandetnik Sep 25 '14 at 12:57

score 0 · Answer 2 · answered Sep 25 '14 at 12:58

You only need to augment your comparison function with the following rules:

if the first value exists in the vector to sort with respect to, but the second value does not exist in it, then first < second
if the second value exists but the first does not, then second < first
if both values exist, compare their index values within that vector

If none of those conditions are true, the existing comparison logic would run.

How do I sort a vector with respect to another vector?

2 Answers2

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