4、np.newaxis的作用
<p>np.newaxis的作用就是在这一位置增加一个一维，这一位置指的是np.newaxis所在的位置，比较抽象，需要配合例子理解。
x1 = np.array([1, 2, 3, 4, 5])</p>
<h1>the shape of x1 is (5,)</h1>
<pre><code>x1_new = x1[:, np.newaxis]
# now, the shape of x1_new is (5, 1)
# array([[1],
# [2],
# [3],
# [4],
# [5]])
x1_new = x1[np.newaxis,:]
# now, the shape of x1_new is (1, 5)
# array([[1, 2, 3, 4, 5]])</code></pre>
<p>再来一个例子
In [124]: arr = np.arange(5*5).reshape(5,5)</p>
<pre><code>In [125]: arr.shape
Out[125]: (5, 5)
array([[ 0, 1, 2, 3, 4],
[ 5, 6, 7, 8, 9],
[10, 11, 12, 13, 14],
[15, 16, 17, 18, 19],
[20, 21, 22, 23, 24]])
# promoting 2D array to a 5D array
In [126]: arr_5D = arr[np.newaxis, ..., np.newaxis, np.newaxis]
In [127]: arr_5D.shape
Out[127]: (1, 5, 5, 1, 1)
array([[[[[ 0]],
[[ 1]],
[[ 2]],
[[ 3]],
[[ 4]]],
[[[ 5]],
[[ 6]],
[[ 7]],
[[ 8]],
[[ 9]]],
[[[10]],
[[11]],
[[12]],
[[13]],
[[14]]],
[[[15]],
[[16]],
[[17]],
[[18]],
[[19]]],
[[[20]],
[[21]],
[[22]],
[[23]],
[[24]]]]])</code></pre>
<p>作者：VanJordan
链接：<a href="https://www.jianshu.com/p/78e1e281f698">https://www.jianshu.com/p/78e1e281f698</a>
来源：简书
简书著作权归作者所有，任何形式的转载都请联系作者获得授权并注明出处。</p>