def sample_following_dist(handle_iter, n, totalf):
    """Samples n passwords following the distribution from the handle
    @handle_iter is an iterator that gives (pw,f) @n is the total
    number of samle asked for @totalf is the total number of users,
    which is euqal to sum(f for pw,f in handle_iter)
    As, handle_iterator is an iterator and can only traverse once, @totalf
    needs to be supplied to the funciton.

    Returns, an array of @n tuples (id, pw) sampled from @handle_iter.
    """
    multiplier = 1.0
    if totalf == 1.0:
        multiplier = 1e8
        # print "WARNING!! I don't except probabilities"

    totalf = totalf * multiplier
    print("# Population Size", totalf)
    A = np.sort(np.unique(np.random.randint(0, totalf, size=n*2))[:n])
    A = A[::-1]
    # Uniqueness check, non necessarily required, but not very
    # computationally intensive
    assert len(A) == n, "Not enough randomnumbers generated"\
        "Requried {}, generated only {}".format(n, len(A))
    j = 0
    sampled = 0
    val = A.pop()
    # print handle_iter
    for _,w,f in handle_iter:
        j += f*multiplier
        if not A: break
        while val<j:
            sampled += 1
            if sampled %5000 == 0:
                print ("Sampled:",sampled)
            yield (val, w)
            if A:
                val = A.pop()
            else:
                break

    print ("# Stopped at:", w, f, j, '\n')
    while A and val<j:
        yield (val, w)
        if A:
            i, val = A.pop()
        else:
            break