努比。Python中的isnan（）-yiteyi-C++库

这个 努比。伊斯南（） 函数测试元素是否为NaN，并以布尔数组的形式返回结果。 语法：

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numpy.isnan(array [, out])

参数：

array : [array_like]Input array or object whose elements, we need to test for infinity
out   : [ndarray, optional]Output array placed with result.
      Its type is preserved and it must be of the right shape to hold the output.

返回：

boolean array containing the result. For scalar input, the result is a new boolean with value
True if the input is positive or negative infinity; otherwise the value is False.
For array input, the result is a boolean array with the same shape as the input and the values
are True where the corresponding element of the input is positive or negative infinity; 
elsewhere the values are False.

代码1：

                       # Python Program illustrating                     
                       # numpy.isnan() method                     
                                
                       import                                  numpy as geek                     
                                
                       print                                  (                                  "Is NaN : "                                  , geek.isnan(                                  1                                  ),                                  ""                                  )                     
                                
                       print                                  (                                  "Is NaN : "                                  , geek.isnan(                                  0                                  ),                                  ""                                  )                     
                                
                       # not a number                     
                       print                                  (                                  "Is NaN : "                                  , geek.isnan(geek.nan),                                  ""                                  )                     
                                
                       #  infinity                     
                       print                                  (                                  "Is NaN : "                                  , geek.isnan(geek.inf),                                  ""                                  )                     
                                
                       print                                  (                                  "Is NaN : "                                  , geek.isnan(geek.NINF),                                  ""                                  )                     
                                
                       x                                  =                                  geek.array([                                  -                                  geek.inf,                                  0.                                  , geek.inf])                     
                       y                                  =                                  geek.array([                                  2                                  ,                                  2                                  ,                                  2                                  ])                     
                       print                                  (                                  "Checking for NaN : "                                  , geek.isnan(x, y))                     
                                

输出：

Is NaN :  False 

Is NaN :  False 

Is NaN :  True 

Is NaN :  False 

Is NaN :  False 

Checking for NaN :  [0 0 0]

代码2：

                       # Python Program illustrating                     
                       # numpy.isnan() method                     
                                
                       import                                  numpy as geek                     
                                
                       # Returns True/False value for each element                     
                       b                                  =                                  geek.arange(                                  20                                  ).reshape(                                  5                                  ,                                  4                                  )                     
                                
                       print                                  (                                  ""                                  ,b)                     
                       print                                  (                                  "Is NaN(Not a Number): "                                  , geek.isnan(b))                     
                                
                                
                       b                                  =                                  [[                                  1j                                  ],                     
                                             [geek.nan]]                     
                       print                                  (                                  "Is NaN(Not a Number) : "                                  , geek.isnan(b))                     

输出：

 [[ 0  1  2  3]
 [ 4  5  6  7]
 [ 8  9 10 11]
 [12 13 14 15]
 [16 17 18 19]]

Is NaN(Not a Number): 
 [[False False False False]
 [False False False False]
 [False False False False]
 [False False False False]
 [False False False False]]

Is NaN(Not a Number) : 
 [[False]
 [ True]]

参考资料： https://docs.scipy.org/doc/numpy-dev/reference/generated/numpy.isnan.html

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