How can I check for NaN values

Question

float  nan   results in Nan  not a number   But how do I check for it  Should be very easy  but I cannot find it

User · Answer

Another method if you re stuck on  lt 2 6  you don t have numpy  and you don t have IEEE 754 support   def isNaN x       return str x     str 1e400 0

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All the methods to tell if the variable is NaN or None   None type  In  1   from numpy import math  In  2   a   None In  3   not a Out 3   True  In  4   len a or        0 Out 4   True  In  5   a    None Out 5   True  In  6   a is None Out 6   True  In  7   a    a Out 7   False  In  9   math isnan a  Traceback  most recent call last     File   lt ipython-input-9-6d4d8c26d370 gt    line 1  in  lt module gt      math isnan a  TypeError  a float is required  In  10   len a     0 Traceback  most recent call last     File   lt ipython-input-10-65b72372873e gt    line 1  in  lt module gt      len a     0 TypeError  object of type  NoneType  has no len     NaN type  In  11   b   float  nan   In  12   b Out 12   nan  In  13   not b Out 13   False  In  14   b    b Out 14   True  In  15   math isnan b  Out 15   True

User · Answer

math isnan x      Return True if x is a NaN  not a number   and False otherwise     gt  gt  gt  import math  gt  gt  gt  x   float  nan    gt  gt  gt  math isnan x  True

User · Answer

Here are three ways where you can test a variable is  quot NaN quot  or not  import pandas as pd import numpy as np import math   For single variable all three libraries return single boolean x1   float  quot nan quot    print f quot It s pd isna     pd isna x1   quot   print f quot It s np isnan     np isnan x1   quot   print f quot It s math isnan    math isnan x1   quot    Output It s pd isna    True It s np isnan    True It s math isnan    True

User · Answer

Well I entered this post  because i ve had some issues with the function   math isnan     There are problem when you run this code   a    hello  math isnan a    It raises exception  My solution for that is to make another check   def is nan x       return isinstance x  float  and math isnan x

User · Answer

I actually just ran into this  but for me it was checking for nan  -inf  or inf  I just used  if float  -inf    lt  float num   lt  float  inf      This is true for numbers  false for nan and both inf  and will raise an exception for things like strings or other types  which is probably a good thing   Also this does not require importing any libraries like math or numpy  numpy is so damn big it doubles the size of any compiled application

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I am receiving the data from a web-service that sends NaN as a string  Nan   But there could be other sorts of string in my data as well  so a simple float value  could throw an exception  I used the following variant of the accepted answer   def isnan value     try        import math       return math isnan float value     except        return False   Requirement   isnan  hello      False isnan  NaN      True isnan 100     False isnan float  nan      True

User · Answer

The usual way to test for a NaN is to see if it s equal to itself   def isNaN num       return num    num

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For nan of type float      gt  gt  gt  import pandas as pd  gt  gt  gt  value   float nan   gt  gt  gt  type value   gt  gt  gt   lt class  float  gt   gt  gt  gt  pd isnull value  True  gt  gt  gt   gt  gt  gt  value    nan   gt  gt  gt  type value   gt  gt  gt   lt class  str  gt   gt  gt  gt  pd isnull value  False

User · Answer

here is an answer working with    NaN implementations respecting IEEE 754 standard    ie  python s NaN  float  nan    numpy nan     any other objects  string or whatever  does not raise exceptions if encountered    A NaN implemented following the standard  is the only value for which the inequality comparison with itself should return True   def is nan x       return  x    x    And some examples   import numpy as np values    float  nan    np nan  55   string   lambda x   x  for value in values      print f  repr value   lt 8     is nan value       Output   nan        True nan        True 55         False  string    False  lt function  lt lambda gt  at 0x000000000927BF28 gt    False

User · Answer

How to remove NaN  float  item s  from a list of mixed data types  If you have mixed types in an iterable  here is a solution that does not use numpy   from math import isnan  Z     a   b   float  NaN     d   float  1 1024      x for x in Z if not                         type x     float   let s drop all float values                          and isnan x        but only if they are nan                              a    b    d   1 1024   Short-circuit evaluation means that isnan will not be called on values that are not of type  float   as False and       quickly evaluates to False without having to evaluate the right-hand side

User · Answer

math isnan    or compare the number to itself  NaN is always    NaN  otherwise  e g  if it is a number  the comparison should succeed

User · Answer

In Python 3 6 checking on a string value x math isnan x  and np isnan x  raises an error   So I can t check if the given value is NaN or not if I don t know beforehand it s a number  The following seems to solve this issue  if str x    nan  and type x    str       print   NaN   else      print   non NaN

User · Answer

numpy isnan number  tells you if it s NaN or not

User · Answer

With python  lt  2 6 I ended up with  def isNaN x       return str float x   lower       nan    This works for me with python 2 5 1 on a Solaris 5 9 box and with python 2 6 5 on Ubuntu 10

User · Answer

for strings in panda take pd isnull   if not pd isnull atext     for word in nltk word tokenize atext     the function as feature extraction for NLTK  def act features atext   features      if not pd isnull atext     for word in nltk word tokenize atext       if word not in default stopwords        features  cont      format word lower     True return features

User · Answer

It seems that checking if it s equal to itself  x  x   is the fastest   import pandas as pd  import numpy as np  import math   x   float  nan     timeit x  x                                                                                                                                                                                                                         44 8 ns    0 152 ns per loop  mean    std  dev  of 7 runs  10000000 loops each    timeit math isnan x                                                                                                                                                                                                                 94 2 ns    0 955 ns per loop  mean    std  dev  of 7 runs  10000000 loops each    timeit pd isna x   281 ns    5 48 ns per loop  mean    std  dev  of 7 runs  1000000 loops each    timeit np isnan x                                                                                                                                                                                                                   1 38   s    15 7 ns per loop  mean    std  dev  of 7 runs  1000000 loops each

[python] How can I check for NaN values?

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