How to sort an vector based on any column value by passing the column index as input?

Question

I have already tried the below code but i want to use this same function for sorting based on different columns.

This given code is sorting based on first column only.

bool sortcol( const vector <int> v1, const vector <int> v2)
{
return v1[0]<v2[0];
}

sort(ArrOfTimings.begin(), ArrOfTimings.end(), sortcol);

Is there any way possible to not make multiple functions but making it all work with one only.

Something like this

bool sortcol(int ind, const vector <int> v1, const vector <int> v2)
{
return v1[ind]<v2[ind];
}

sort(ArrOfTimings.begin(), ArrOfTimings.end(), sortcol(0));

Answer 1

You cannot pass additional info to a free function used for comparison for std::sort by means other than global data.

You can create a struct with a member variable storing the column to compare in addition to providing a call operator for comparing the values though.

I'd prefer a lambda, since it results in shorter code though: Simply capture the index.

Note: It's also beneficial to avoid copying the vector by using references as parameters.

void SortByColumn(std::vector<std::vector<int>> & data, size_t column)
{
    std::sort(data.begin(), data.end(),
              [column](std::vector<int> const& v1, std::vector<int> const& v2)
              {
                  return v1[column] < v2[column];
              });
}