Initialize multidimensional array in Python?

Question

I want to initialize a multidimensional array. My goal is as follows:

initialize array:
```
maps = np.array([])
```

add a number of 2D matrices with different sizes to the initialized array

for i in range(0,3):   
   maps = [maps some_matrix]

maps = [array[3x4], array[4x4], array[6x4]]

The answer is in this post : http://stackoverflow.com/questions/6667201/how-to-define-two-dimensional-array-in-python — Derlin, Jan 26 '16 at 21:38
@ juan .. how will you create a array which contains several 2D arrays with different dimensions — Free Man, Jan 26 '16 at 22:26

score 0 · Answer 1 · answered Jan 27 '16 at 00:20

Define a list containing 3 different arrays:

In [241]: ll = [np.ones((3,4),int), np.zeros((2,4),bool), np.arange(6).reshape(2,3)]
In [242]: ll
Out[242]: 
    [array([[1, 1, 1, 1],
            [1, 1, 1, 1],
            [1, 1, 1, 1]]), 
     array([[False, False, False, False],
            [False, False, False, False]], dtype=bool), 
     array([[0, 1, 2],
            [3, 4, 5]])]

I could wrap that list in array:

 In [243]: np.array(ll)
 Out[243]: 
 array([array([[1, 1, 1, 1],
       [1, 1, 1, 1],
       [1, 1, 1, 1]]),
       array([[False, False, False, False],
       [False, False, False, False]], dtype=bool),
       array([[0, 1, 2],
       [3, 4, 5]])], dtype=object)

Notice the dtype of the outer array is object. In other words, the array is shape (3,), and contains pointers to objects elsewhere. I could replace any of those arrays with other python objects - None, a list, a number, or a dictionary.

Don't go this route unless you really need an object type array. For most purposes the list is just as good if not better. Lists are the original Python structure for holding a diverse collection of objects. Arrays are designed to hold a fixed number of homogeneous objects such as numbers. It's bad practice to start with a small empty array and try to grow it.

Initialize multidimensional array in Python?

1 Answers1