Growing matrices columnwise in NumPy

Question

In pure Python you can grow matrices column by column pretty easily:

data = []
for i in something:
    newColumn = getColumnDataAsList(i)
    data.append(newColu         


        

Answer 1

The hstack can work on zero sized arrays:

import numpy as np

N = 5
M = 15

a = np.ndarray(shape = (N, 0))
for i in range(M):
    b = np.random.rand(N, 1)
    a = np.hstack((a, b))