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numpy.ndarrayの連結

Posted at

以下記事を参考にしています。
http://tanukigraph.hatenablog.com/entry/2017/08/23/195756

忘れやすいのでメモ。

import numpy as np

a = np.array([[1,2],[3,4]])
b = np.array([[5,6],[7,8]])
c = np.array([[1,2],[3,4],[5,6]])

1. (2,2)×2 -> (4,2)

np.concatenate([a,b],axis=0)

# output
array([[1, 2],
       [3, 4],
       [5, 6],
       [7, 8]])

※concatnateで次元を上げることはできない

2. (2,2)×2 -> (2,2,2)

パターン1

np.stack([a,b],axis=0)

# output
array([[[1, 2],
        [3, 4]],

       [[5, 6],
        [7, 8]]])

パターン2

np.stack([a,b],axis=1)

array([[[1, 2],
        [5, 6]],

       [[3, 4],
        [7, 8]]])
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