How to extend an array in-place in Numpy?

Question

Currently, I have some code like this

import numpy as np
ret = np.array([])
for i in range(100000):
  tmp =  get_input(i)
  ret = np.append(ret, np.zeros(len         


        

Answer 1

You can use the .resize() method of ndarrays. It requires that the memory is not referred to by other arrays/variables.

import numpy as np
ret = np.array([])
for i in range(100):
    tmp = np.random.rand(np.random.randint(1, 100))
    ret.resize(len(ret) + len(tmp)) # <- ret is not referred to by anything else,
                                    #    so this works
    ret[-len(tmp):] = tmp

The efficiency can be improved by using the usual array memory overrallocation schemes.