Generating nested Numpy Arrays

Question

I'm trying to write a function that will take as input a numpy array in the form:

a = [[0,0], [10,0], [10,10], [5,4]]

and return a numpy array b such that:

b = [[[0,0]], [[10,0]], [[10,10]], [[5,4]]]

For some reason I'm finding this surprisingly difficult.

The reason I'm doing this is that I have some contours generated using skimage that I'm attempting to use opencv2 on to calculate features ( area, perimeter etc...) but the opencv functions will only take arrays in the form of b as input, rather than a.

hpaulj · Accepted Answer · 2017-03-30 17:39:59Z

2

a is shape (4,2), b is (4,1,2)

a.reshape(4,1,2)
np.expanddims(a, 1)
a[:,None]

all work

In [503]: B
Out[503]: 
array([[[ 0,  0]],

       [[10,  0]],

       [[10, 10]],

       [[ 5,  4]]])
In [504]: B.tolist()
Out[504]: [[[0, 0]], [[10, 0]], [[10, 10]], [[5, 4]]]

answered Mar 30, 2017 at 17:39

hpaulj

233k14 gold badges260 silver badges392 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Generating nested Numpy Arrays

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related