numpy：FutureWarning：元素比较失败

Question

对于此 SO 帖子 FutureWarning: elementwise comparison failed; returning scalar, but in the future will perform elementwise comparison 中描述的问题，numpy 中是否有任何解决方案。我的 numpy 版本是 1.19.1 并使用 python 3.8.5。

a = np.array(['aug', False, False, False])

a == 'aug'

array([ True, False, False, False])

但是：

a == False

<ipython-input-88-f9ff25cfe387>:1: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison
  a == False

与 np.nan 相同：

a = array(['aug', np.nan, np.nan, np.nan])
a == 'aug'

array([ True, False, False, False])

但是：

a == np.nan

<ipython-input-1236-9224919e9367>:1: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison
  a == np.nan

False

Answer 1

创建后查看数组：

In [58]: a = np.array(['aug', False, False, False])
    ...: 
In [59]: a
Out[59]: array(['aug', 'False', 'False', 'False'], dtype='<U5')
In [60]: a == 'aug'
Out[60]: array([ True, False, False, False])
In [61]: a == False
<ipython-input-61-f9ff25cfe387>:1: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison
  a == False
Out[61]: False
In [62]: a == 'False'
Out[62]: array([False,  True,  True,  True])

这是一个字符串 dtype 数组。测试匹配字符串有效。测试非字符串值是错误的。

nan 也一样：

In [64]: a = np.array(['aug', np.nan, np.nan, np.nan])
In [65]: a
Out[65]: array(['aug', 'nan', 'nan', 'nan'], dtype='<U3')
In [66]: a == 'nan'
Out[66]: array([False,  True,  True,  True])

如果您必须混合类型 - 字符串、布尔值、浮点数，您可以指定 object dtype。这使得数组更像列表。

In [67]: a = np.array(['aug', False, False, False], object)
In [68]: a
Out[68]: array(['aug', False, False, False], dtype=object)
In [69]: a == 'aug'
Out[69]: array([ True, False, False, False])
In [70]: a == False
Out[70]: array([False,  True,  True,  True])
In [71]: a == True
Out[71]: array([False, False, False, False])

但这对np.nan 没有帮助。 nan 是一种特殊的浮点数，它不等于任何东西，甚至不等于它自己。

In [72]: a = np.array(['aug', np.nan, np.nan, np.nan], object)
In [73]: a
Out[73]: array(['aug', nan, nan, nan], dtype=object)
In [74]: a=='aug'
Out[74]: array([ True, False, False, False])
In [75]: a == np.nan
Out[75]: array([False, False, False, False])

isnan 是测试nan 的正确方法，但它仅适用于 float dtype 数组：

In [76]: np.isnan(a)
Traceback (most recent call last):
  File "<ipython-input-76-da86cb21b8a4>", line 1, in <module>
    np.isnan(a)
TypeError: ufunc 'isnan' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''