Remove NaN value from a set

Question

Is it possible to easily remove NaN values for a Python Set object? Given that NaN values do not equal anything (and float('nan') is float('nan') is also False), you can end up with many NaN values in a Set.

>>> a = set( (float('nan'), float('nan'), 'a') )
>>> a
{nan, nan, 'a'}

The best I can come up with it to define a function like math.isnan, but that is tolerant of non-float types like:

def my_isnan(x):
    try:
        return math.isnan(x)
    except TypeError:
        return False

Then you can use a set comprehension like this:

>>> {x for x in a if not my_isnan(x)}
{'a'}

Asked By: Brad Campbell

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Source

Answer 1

In practice, you could look at the fact that nan != nan as a feature, not a bug:

>>> a = {float('nan'), float('nan'), 'a'}
>>> a
{nan, nan, 'a'}
>>> {x for x in a if x==x}
{'a'}

On the positive side, no need for a helper function. On the negative side, if you have a non-nan object which is also not equal to itself, you’ll remove that too.

Answered By: DSM

Answer 2

Also you can use filter:

In[75]: a = set((float('nan'), float('nan'), 'a'))

In[76]: set(filter(lambda x: x == x , a))
Out[76]: {'a'}

Answered By: ej_f

Answer 3

Use pd.notna() from pandas, e.g.:

In [219]: import pandas as pd

In [220]: a = set((float('nan'), float('nan'), 'a'))

In [221]: a = {x for x in a if pd.notna(x)}

In [222]: a
Out[222]: {'a'}

Answered By: Pawel Kranzberg

Answer 4

We can simply use the .remove() method

In[1]: a = set([np.nan, "A"])
In[2]: a
Out: {'A', nan}
In[3]: a.remove(np.nan)
In[4]: a
Out: {'A'}

Answered By: Benoît Lebreton

Remove NaN value from a set

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