Lazily stack matrices

stacking_matrices.py

import numpy as np

"""Stacking as we loop"""

%%timeit -n 10
res = None
for i in range(100):
    batch = np.random.random((100, 100))
    if res is None:
        res = batch
    else:
        res = np.vstack((res, batch))
# 279 ms ± 15 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)
        
    
"""Stacking after the loop"""

%%timeit -n 10
res = []
for i in range(100):
    res.append(np.random.random((100, 100)))
    
res = np.vstack(res)
# 14 ms ± 657 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)