利用numpy的newaxis轉變矩陣的形狀

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title: hange shape of matrix by numpy
tags: python, numpy

簡單筆記一下：
有一個一維陣列x1，我分別想要把它變成一個3*1的矩陣x2，以及1*3的矩陣x3，作法如下。

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import numpy as np
x1 = np.array([10, 20, 30], float)
print "shape of x1 is ", x1.shape
print x1

x2 = x1[:, np.newaxis]
print "shape of x2 is ", x2.shape
print x2

x3 = x1[np.newaxis, :]
print "shape of x3 is ", x2.shape
print x2

---result---
shape of x1 is  (3,)
[ 10.  20.  30.]
shape of x2 is  (3, 1)
[[ 10.]
 [ 20.]
 [ 30.]]
shape of x3 is  (3, 1)
[[ 10.]
 [ 20.]
 [ 30.]]