JohnAndrews -4 years ago 610

Python Question

I have a list of strings

`x = ['A', 'B', nan, 'D']`

and want to remove the nan.

I tried:

`x = x[~numpy.isnan(x)]`

But that only works if it contains numbers. How do we solve this for strings in Python 3+?

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Answer Source

If you have a numpy array you can simply check the item is not the string `nan`

, but if you have a list you can check the identity with `is`

and `np.nan`

since it's a singleton object.

```
In [25]: x = np.array(['A', 'B', np.nan, 'D'])
In [26]: x
Out[26]:
array(['A', 'B', 'nan', 'D'],
dtype='<U3')
In [27]: x[x != 'nan']
Out[27]:
array(['A', 'B', 'D'],
dtype='<U3')
In [28]: x = ['A', 'B', np.nan, 'D']
In [30]: [i for i in x if i is not np.nan]
Out[30]: ['A', 'B', 'D']
```

Or as a functional approach in case you have a python list:

```
In [34]: from operator import is_not
In [35]: from functools import partial
In [37]: f = partial(is_not, np.nan)
In [38]: x = ['A', 'B', np.nan, 'D']
In [39]: list(filter(f, x))
Out[39]: ['A', 'B', 'D']
```

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