Expand Numpy Matrix

I am trying to somehow expand numpy matrices, which typically look like: import numpy as np mtx = np.matrix([[['a','b','c'], ['x'], 3], [['d','e','f'], ['y'], 2], [['g','h','i

Solution 1:

You could use np.repeat to repeat the first two columns of each row mtx[:,:2] the number of times given by the corresponding row of the third column arr[:,2]:

>>> arr = np.asarray(mtx)
>>> np.repeat(arr[:,:2], arr[:,2].astype(int), axis=0)
array([[['a', 'b', 'c'], ['x']],
       [['a', 'b', 'c'], ['x']],
       [['a', 'b', 'c'], ['x']],
       [['d', 'e', 'f'], ['y']],
       [['d', 'e', 'f'], ['y']],
       [['g', 'h', 'i'], ['z']]], dtype=object)

The third column needs to be cast to integer values first (e.g. using astype(int)). I also found it necessary to treat mtx as an array for this to work: you can easily turn it back into a matrix object again with np.matrix.