Question

I have a problem sorting vectors in 2D vector? I would like to sort them based on their capacity from the largest to the smallest.

Example: ROWS {{1,2,3},{1,2},{1,2,3,4,5}}

it should be sorted as ROWS.capacity(); // ROWS {{1,2,3,4,5},{1,2,3},{1,2}}

The following is part of the code i did until now:

 std::vector< std::vector<int> >::iterator row;
 std::vector<int>::iterator col;



for (row=ROWS.begin(); row<ROWS.end(); row++){

Logger::logln(LOG_DEBUG, "ROW: %d",row->capacity());

     for (col = row->begin(); col != row->end(); col++){
         Logger::logln(LOG_DEBUG, " CONTENT: %d  ",*col);
     }
 }

i need to the following:
if(row1.capacity > row2.capacity)
then swap or something like this.

Thanks in advance 🙂

Answer 1

You could use std::sort with a custom ordering predicate:

struct CapacityGreater : public std::binary_function<std::vector<int>,
                                                     std::vector<int>,bool>
{
    bool operator()(const std::vector<int> &a, const std::vector<int> &b) const
        { return a.capacity() > b.capacity(); }
};

std::sort(ROWS.begin(), ROWS.end(), CapacityGreater());

This should work well if std::sort uses std::swap internally, otherwise the copying of rows could get quite expensive and you probably need to implement your own sorting function.

You should also think, if you really need capacity() and not size().