Making 2 dimensional numpy array with two 1 dimensional array

Question

I would like to convert 2 numpy arrays such as these ones:

a = [[1, 2, 3]]
b = [[100, 200, 300]]

to an array like below.

[[1, 100], [1, 200], [1, 300], [2, 100], [2, 200], [3, 300], [3, 100], [3, 200], [3, 300]]

Is this possible in NumPy?

Thanks in advance.

(edited to clarify the point of this question.) I'm trying to find a numpy way of solution.

Possible duplicate of Get the cartesian product of a series of lists? — Kasravnd
– Kasravnd, Commented Dec 13, 2018 at 11:00
Guys, this is for numpy arrays, not Python lists or dictionaries. — Matthieu Brucher
– Matthieu Brucher, Commented Dec 13, 2018 at 11:04
a and b are lists, as is the desired result. The itertools. product works fine (though it produces a list of tuples). — hpaulj
– hpaulj, Commented Dec 13, 2018 at 17:04

Matthieu Brucher · Accepted Answer · 2018-12-13 11:03:54Z

1

This is a job for meshgrid and stack:

a = np.array([ [1, 2, 3] ])
b = np.array([ [100, 200, 300] ])

print(np.stack(np.meshgrid(a, b)).T.reshape(-1,2))

The first creates a tuple of coordinate on the grid, the second stacks them. Then you just need to transpose and flatten.

answered Dec 13, 2018 at 11:03

Matthieu Brucher

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This is what I've been trying to find out. Thanks for your answer.