python中numpy数组的len()
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len() of a numpy array in python
提问by Monica Heddneck
If I use len(np.array([[2,3,1,0], [2,3,1,0], [3,2,1,1]])), I get back 3.
如果我使用len(np.array([[2,3,1,0], [2,3,1,0], [3,2,1,1]]))，我会返回 3。
Why is there no argument for len()about which axis I want the length of in multidimensional arrays? This is alarming. Is there an alternative?
为什么没有len()关于我想要多维数组中哪个轴的长度的争论？这令人担忧。有替代方案吗？
回答by hpaulj
What is the lenof the equivalent nested list?
什么是len等效嵌套列表？
len([[2,3,1,0], [2,3,1,0], [3,2,1,1]])
With the more general concept of shape, numpydevelopers choose to implement __len__as the first dimension. Python maps len(obj)onto obj.__len__.
有了更一般的概念shape，numpy开发人员选择实现__len__作为第一个维度。Python 映射len(obj)到obj.__len__.
X.shapereturns a tuple, which does have a len- which is the number of dimensions, X.ndim. X.shape[i]selects the ithdimension (a straight forward application of tuple indexing).
X.shape返回一个元组，它有一个len- 这是维数，X.ndim。 X.shape[i]选择ith维度（元组索引的直接应用）。
回答by Dmitry Pleshkov
Easy. Use .shape.
简单。使用.shape.
>>> nparray.shape
(5, 6) #Returns a tuple of array dimensions.
回答by Batman
You can transpose the array if you want to get the length of the other dimension.
如果您想获得另一个维度的长度，您可以转置数组。
len(np.array([[2,3,1,0], [2,3,1,0], [3,2,1,1]]).T)
