Randomizing multidimensional vectors/arrays

[Lindley]

Okay, so it's random rearrangement rather than random selection.

There are two primary approaches you can use:

1) Define a2 in such a way that its memory is contiguous (it is not presently), then use random_shuffle on the entire range. A boost::multi_array is one easy way to do this, or you could use a vector<int> for the underlying data and a vector<int*> to represent the rows. There's lots of material on different ways to define 2D arrays around.

2) Keep a2 as-is, but shuffle a 1D array of 2D indexes into it. For instance,

vector<pair<int,int>> inds;
inds.push_back(make_pair(0,0));
inds.push_back(make_pair(0,1));
...
inds.push_back(make_pair(3,2));
inds.push_back(make_pair(3,3));

random_shuffle(inds.begin(),inds.end());

for (unsigned i = 0; i < inds.size(); ++i)
{
    unsigned row = i/4;
    unsigned col = i&#37;4;
    a2[row][col] = a[inds[i].first][inds[i].second];
}

(not tested)