CODEWITHSUNDEEP
pythonnumpy
pnodbnda
pnodbnda

Reputation: 659

Why can't I create a numpy array like this: array([1, 2], 3)

from numpy import array
test_list = [[1,2],3]
x = array(test_list) #ValueError: setting an array element with a sequence.

Basically, I have a point with 2 coordinates and a scale and I was trying to put several on a ndarray but I can't do it right now. I could just use [1,2,3] but I'm curious about why I can't store that type of list in an array.

Upvotes: 2

Views: 4264

Answers (3)

DerWeh
DerWeh

Reputation: 1821

If you really need non-rectangular arrays, you can give awkward a try:

In [1]: import awkward

In [2]: test_list = [[1,2],3]

In [3]: x = awkward.fromiter(test_list) 

In [4]: x
Out[4]: <UnionArray [[1 2] 3] at 0x7f69c087c390>

In [5]: x + 1
Out[5]: <UnionArray [[2 3] 4] at 0x7f69c08075c0>

In [6]: x[0]
Out[6]: array([1, 2])

In [7]: x[0, 1]
Out[7]: 2

It behaves in many ways like a numpy array.

Upvotes: 0

Ben
Ben

Reputation: 9703

You can do

x = array([[1,2],3], dtype=object_)

which gives you a an array with a generic "object" dtype. But that doesn't get you very far. Even if you did

x = array([array([1,2]),3], dtype=object_)

you would have x[0] be an array, but you still couldn't index x[0,0], you'd have to do x[0][0].

It's a shame; there are places where it would be useful to do things like this and then do x.sum(1) and get [3, 3] as the result. (You can always do map(sum, x).)

Upvotes: -1

moinudin
moinudin

Reputation: 138347

It's failing because the array is non-rectangular. If we change the 3 to [3, 4] then it works.

>>> array([[1, 2], [3, 4]])
array([[1, 2],
       [3, 4]])

Upvotes: 3

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