Python:How to assign a list or an array to an array element?

Question

My code requires me to replace elements of an array of dimension 3x3 with a list or array of a certain dimension. How can I achieve that? When I write my code, it throws an error stating that:

ValueError: setting an array element with a sequence.

My code:

import numpy as np
Y=np.array([1,2,3,4,5,6,7,1,2,3,4,5,6,7,1,2,4])
c_g=np.array([[[1,2],[2,3]],[[4,5],[1,6]]])
xx=[1,2,3]
var=2
theta_g=np.zeros((c_g.shape[0],c_g.shape[1]))
for i in range(c_g.shape[0]):
    for j in range(c_g.shape[1]):
         theta_g[i][j]=Y[var:var+len(c_g[i][j])**len(xx)]
         #here Y is some one dimensional array or list which I want to //
         #assign to each element of theta_g
         var=var+len(c_g[i][j])**len(xx)
print theta_g

In the code above I want to manipulate theta_g . In fact, I want to assign an array to each element of theta_g. How can I accomplish that? Desired Output: theta_g which is a matrix of dimension equal to that of c_g .

Answer 1

You can use np.stack .

  >>> a = [np.array([1, 2]), np.array([3, 4])]
  >>> np.stack(a)
  array([[1, 2],
           [3, 4]])

Answer 2

I think you should just specify the type of the elements of the array as np.ndarray or list , like so:

theta_g=np.zeros((c_g.shape[0],c_g.shape[1]), dtype=np.ndarray)

Because you didn't really explain the logic of assignment, let me demonstrate in my own example, where I assign some arrays to a 2x2 array:

from itertools import product
Y = np.array([0,0,1,2,10,20])
Z = np.zeros((2,2), dtype=np.ndarray)
for i,j in product(range(0,2), repeat = 2):
    Z[i,j] = Y[2*(i+j):2+2*(i+j)]
print(Z)

prints

[[array([0, 0]) array([1, 2])] [array([1, 2]) array([10, 20])]]