I cannot access the values of an index position that has a nan in it and wonder how I could solve this. (In my project this index has a very special meaning and I really need to keep it, otherwise I would need to make some dirty manual modifications: “there is always a solution” even if it is a very bad one).
df
Out
temp_playlist objId
0 o1 [0, 6]
o2 [1, 4]
o3 [2, 5]
o4 [8, 9, 12]
o5 [10, 13]
o6 [11, 14]
NaN [3, 7]
Name: x, dtype: object
df.index
Out
MultiIndex([(0, 'o1'),
(0, 'o2'),
(0, 'o3'),
(0, 'o4'),
(0, 'o5'),
(0, 'o6'),
(0, nan)],
names=['temp_playlist', 'objId'])
Now I want to access the [3, 7] values as df.loc[(0, np.nan)] and obtain the KeyError: (0, nan) error.
Just to put it in perspective: [df.loc[idx] for idx in df.index if not pd.isna(idx[1])] works properly because I am skipping the problematic index.
What am I missing and how could I solve this?
(Windows 10, python 3.8.5, pandas 1.3.1, numpy 1.20.3, reported to pandas here)
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Answer
Update
I am able to reproduce your error after grouping and aggregating a data frame.
>>> import pandas as pd
>>> data = pd.DataFrame({
... "temp_playlist": [0] * 15,
... "objId": ['o1'] * 2 + ['o2'] * 2 + ['o3'] * 2 + ['o4'] * 3 + ['o5'] * 2 + ['o6'] * 2 + [pd.NA] * 2,
... "vals": [0, 6, 1, 4, 2, 5, 8, 9, 12, 10, 13, 11, 14, 3, 7]
... })
>>> df = data.groupby(["temp_playlist", "objId"], dropna=False).agg(list)
>>> df.loc[(0, pd.NA)]
Traceback (most recent call last):
File "/home/ec2-user/miniconda3/envs/so-pandas-nan-index/lib/python3.8/site-packages/pandas/core/indexes/base.py", line 3361, in get_loc
return self._engine.get_loc(casted_key)
File "pandas/_libs/index.pyx", line 76, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/index.pyx", line 108, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/hashtable_class_helper.pxi", line 5198, in pandas._libs.hashtable.PyObjectHashTable.get_item
File "pandas/_libs/hashtable_class_helper.pxi", line 5206, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: <NA>
Passing in an explit MultiIndex works, though.
>>> df.loc[pd.MultiIndex.from_tuples([(0, pd.NA)], names=["temp_playlist", "objId"])]
vals
temp_playlist objId
0 NaN [3, 7]
>>> df.loc[pd.MultiIndex.from_tuples([(0, pd.NA)])]
vals
0 NaN [3, 7]
And so does returning a data frame using a single tuple. Note using [[]] returns a DataFrame.
>>> df.loc[[(0, pd.NA)]]
vals
temp_playlist objId
0 NaN [3, 7]
As does DataFrame.reindex (see also the user guide on reindexing).
>>> df.reindex([(0, pd.NA)])
vals
temp_playlist objId
0 NaN [3, 7]
Original Attempt to Reproduce Error
I am not able to reproduce your error. You can see below that using df.loc[(0, np.nan)] works.
Python 3.8.5 (default, Sep 4 2020, 07:30:14)
[GCC 7.3.0] :: Anaconda, Inc. on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy as np
>>> import pandas as pd
>>> nan_index = pd.MultiIndex.from_tuples([(0, 'o1'),
(0, 'o2'),
(0, 'o3'),
(0, 'o4'),
(0, 'o5'),
(0, 'o6'),
(0, np.nan)])
>>> print(nan_index)
MultiIndex([(0, 'o1'),
(0, 'o2'),
(0, 'o3'),
(0, 'o4'),
(0, 'o5'),
(0, 'o6'),
(0, nan)],
)
>>> rng = np.random.default_rng(42)
>>> vals = [rng.choice(20, 2) for i in range(nan_index.shape[0])]
>>> print(vals)
[array([ 1, 15]), array([13, 8]), array([ 8, 17]), array([ 1, 13]), array([4, 1]), array([10, 19]), array([14, 15])]
>>> df = pd.DataFrame({"vals": vals}, index=nan_index)
>>> print(df)
vals
0 o1 [1, 15]
o2 [13, 8]
o3 [8, 17]
o4 [1, 13]
o5 [4, 1]
o6 [10, 19]
NaN [14, 15]
>>> print(df.loc[(0, 'o1')])
vals [1, 15]
Name: (0, o1), dtype: object
>>> print(df.loc[(0, np.nan)])
vals [14, 15]
Name: (0, nan), dtype: object
>>> print(pd.__version__)
1.3.1
Then I noticed that your index was printed as (0, nan) but mine was (0, np.nan). The difference was that I used np.nan and I suspect yours is pd.NA.
>>> nan_index = pd.MultiIndex.from_tuples([(0, 'o1'),
(0, 'o2'),
(0, 'o3'),
(0, 'o4'),
(0, 'o5'),
(0, 'o6'),
(0, pd.NA)])
>>> nan_index
MultiIndex([(0, 'o1'),
(0, 'o2'),
(0, 'o3'),
(0, 'o4'),
(0, 'o5'),
(0, 'o6'),
(0, nan)],
)
>>> df = pd.DataFrame({"vals": vals}, index=nan_index)
>>> df
vals
0 o1 [1, 15]
o2 [13, 8]
o3 [8, 17]
o4 [1, 13]
o5 [4, 1]
o6 [10, 19]
NaN [14, 15]
However, that did not resolve the difference. I was still able to use df.loc[(0, np.nan)].
>>> df.loc[(0, pd.NA)] vals [14, 15] Name: (0, nan), dtype: object >>> df.loc[(0, np.nan)] vals [14, 15] Name: (0, nan), dtype: object
Moreover, I was also able to use df.loc[(0, None)].
>>> df.loc[(0, None)] vals [14, 15] Name: (0, nan), dtype: object
Just to confirm, np.nan, pd.NA, and None are all different objects. Pandas must treat them the same when used with DataFrame.loc.
>>> pd.NA is np.nan False >>> pd.NA is None False >>> np.nan is None False >>> type(pd.NA) <class 'pandas._libs.missing.NAType'> >>> type(np.nan) <class 'float'>