Numpy.VisibleDeproationWarning：从不整齐的嵌套序列创建ndarray [英] numpy.VisibleDeprecationWarning: Creating an ndarray from ragged nested sequences

问题描述

这里有一个我无法理解的行为例子，也许有人可以分享一下它背后的逻辑：

ccn = np.ones(1)
bbb = 7
bbn = np.array(bbb)
bbn * ccn # this is OK
    array([7.])
np.prod((bbn,ccn)) # but this is NOT
    Traceback (most recent call last):
    File "C:Program FilesJetBrainsPyCharm Community Edition 2020.2.2pluginspython-cehelperspydev\_pydevd_bundlepydevd_exec2.py", line 3, in Exec
    exec(exp, global_vars, local_vars)
  File "<input>", line 1, in <module>
  File "<__array_function__ internals>", line 5, in prod
  File "C:Users...venvlibsite-packages
umpycorefromnumeric.py", line 2999, in prod
    return _wrapreduction(a, np.multiply, 'prod', axis, dtype, out,
  File "C:Users...venvlibsite-packages
umpycorefromnumeric.py", line 87, in _wrapreduction
    return ufunc.reduce(obj, axis, dtype, out, **passkwargs)
numpy.VisibleDeprecationWarning: Creating an ndarray from ragged nested sequences (which is a list-or-tuple of lists-or-tuples-or ndarrays with different lengths or shapes) is deprecated. If you meant to do this, you must specify 'dtype=object' when creating the ndarray

为什么？为什么两个数字的简单相乘会是个问题？就形式代数而言，没有维度问题，也没有数据类型问题？结果总是一个单独的数字，不可能突然变成矢量或物体。prod(a,b)对于a和b是标量或1x1；矩阵；这是MatLab或Octave不会遇到的问题。

我知道我可以关闭此错误等，但为什么它是偶数和错误？

推荐答案

In [346]: ccn = np.ones(1)
     ...: bbb = 7
     ...: bbn = np.array(bbb)
In [347]: ccn.shape
Out[347]: (1,)
In [348]: bbn.shape
Out[348]: ()
In [349]: np.array((bbn,ccn))
<ipython-input-349-997419ba7a2f>:1: VisibleDeprecationWarning: Creating an ndarray from ragged nested sequences (which is a list-or-tuple of lists-or-tuples-or ndarrays with different lengths or shapes) is deprecated. If you meant to do this, you must specify 'dtype=object' when creating the ndarray
  np.array((bbn,ccn))
Out[349]: array([array(7), array([1.])], dtype=object)

您有不同维度的数组，不能合并为一个数值数组。

<2-3]>表达式实际上是：

np.multiply.reduce(np.array([bbn,ccn]))

可以从您的回溯中推断。

在八度音阶中，两个对象都有形状(1，1)，2D

>> ccn = ones(1)
ccn =  1
>> ccn = ones(1);
>> size(ccn)
ans =

   1   1

>> bbn = 7;
>> size(bbn)
ans =

   1   1

>> [bbn,ccn]
ans =

   7   1

它没有真正的标量；所有东西都是2D的(即使3D也是最后一个维度上的模糊处理)。

和‘原始’的Python输入：

In [350]: np.array([1,[1]])
<ipython-input-350-f17372e1b22d>:1: VisibleDeprecationWarning: ...
  np.array([1,[1]])
Out[350]: array([1, list([1])], dtype=object)

对象dtype数组保留输入的类型。

编辑

prod不是简单的乘法。这是一个减法运算，就像数学中的大圆周率。即使在八度音阶中也不是：

>> prod([[2,3],[3;4]])
error: horizontal dimensions mismatch (1x2 vs 2x1)
>> [2,3]*[3;4]
ans =  18
>> [2,3].*[3;4]
ans =

    6    9
    8   12

NumPy等效项：

In [97]: np.prod((np.array([2,3]),np.array([[3],[4]])))
/usr/local/lib/python3.8/dist-packages/numpy/core/fromnumeric.py:87: VisibleDeprecationWarning: Creating an ndarray from ragged nested sequences...
    return ufunc.reduce(obj, axis, dtype, out, **passkwargs)
ValueError: could not broadcast input array from shape (2,1) into shape (2,)

In [98]: np.array([2,3])@np.array([[3],[4]])
Out[98]: array([18])
In [99]: np.array([2,3])*np.array([[3],[4]])
Out[99]: 
array([[ 6,  9],
       [ 8, 12]])

该警告和此处的错误是在尝试从(np.array([2,3]),np.array([[3],[4]]))生成一个数组时生成的。

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