sorting problem

[baxy]

Hi,

let say my situation is the following. I have two vectors one of which is a vector of vectors:

vector<int> v1;

vector<vector<int>> v2;

in v1 contains index positions of vectors in v2:

v1:

0
1
2
3


v2:

0-> 8 5 6 4 2
1-> 7 6
2-> 81 1 91 9 1 1 2 3 54 1 
3-> 1

what i need to do is to sort v2 according to the size of vectors in it v2[i].size() and accordingly v1 such that:

after sort:


v2:

0-> 1
1-> 7 6
2-> 8 5 6 4 2
3-> 81 1 91 9 1 1 2 3 54 1

and v1:

3
1
0
2

any clever solution to this problem ??

[Aslaville]

You can set your predicate to do exactly what you want...

[laserlight]

I suggest combining each inner vector with its original index:

struct ItemsIndexPair
{
    std::vector<int> items;
    std::size_t index;
};

Then you can do something like this:

std::vector<ItemsIndexPair> all_items;
all_items.push_back({{8, 5, 6, 4, 2}, all_items.size()});
all_items.push_back({{7, 6}, all_items.size()});
// ...

std::sort(
    all_items.begin(),
    all_items.end(),
    [](const ItemsIndexPair& lhs, const ItemsIndexPair& rhs) {
        return lhs.items.size() < rhs.items.size();
    }
);