python - balance positives and negatives in numpy -

i have matrix last column has floats in it. around 70% of numbers positive, while 30% negative. i'd remove rows positive number result matrix has approxiamtely same number of positive , negative numbers in last column. i'd remove positives rows randomly.

what this:

import numpy np  x = np.arange(30).reshape(10, 3)  x[[0,1,2,],[2,2,2]] = x[[0,1,2],[2,2,2]] * -1  = np.where(x[:,2] > 0)[0]  n_pos = np.sum(x[:,2] > 0) n_neg = np.sum(x[:,2] < 0)  n_to_remove = n_pos - n_neg np.random.shuffle(a)  new_x = np.delete(x, a[:n_to_remove], axis = 0) 

result:

>>> x  array([[ 0,  1, -2],        [ 3,  4, -5],        [ 6,  7, -8],        [ 9, 10, 11],        [12, 13, 14],        [15, 16, 17],        [18, 19, 20],        [21, 22, 23],        [24, 25, 26],        [27, 28, 29]]) >>> new_x array([[ 0,  1, -2],        [ 3,  4, -5],        [ 6,  7, -8],        [15, 16, 17],        [18, 19, 20],        [27, 28, 29]]) 

i think easier arrays matrices, let me know if need solution matrices.