Python Pandas: check if items from list is in df index

Question

I have a dataframe:

data = {'year': [2010, 2011, 2012, 2011, 2012, 2010, 2011, 2012],
    'team': ['Bears', 'Bears', 'Bears', 'Packers', 'Packers', 'Lions', 'Lions', 'Lions'],
    'wins': ['11102', '8425', '12%', '15%', '11%', '6%', '20%', '4%'],
    'losses': ['5222', '8888', '6%', '1%', '5%', '30%', '6%', '12%'],
    }
football = pd.DataFrame(data, index=['a','b','c','d','e','f','g','ssa'], columns=['year', 'team', 'wins', 'losses'])

I also have a list:

fixed_cats = ['d','g','ssa']

I would like to check if the items from the fixed_cats list are found at the bottom of the df's index.

Here is my failed attempt:

football.loc[football.index[-len(fixed_cats):].isin(fixed_cats)]

for some reason, this returns a df with the index ['b','c'].

Expected output:

a df with the index of 'g' and 'ssa'

Answer 1

The reason you saw ['b','c'] in your first attempt is that what is returned from the inner isin is a boolean index of [False, True, True] which you're applying to the df from the beginning, you need to reapply it again to the last 3 rows:

In [21]:

fixed_cats = ['d','g','ssa']
football[-len(fixed_cats):][football.index[-len(fixed_cats):].isin(fixed_cats)]
Out[21]:
     year   team wins losses
g    2011  Lions  20%     6%
ssa  2012  Lions   4%    12%

In [22]:

football.index[-len(fixed_cats):].isin(fixed_cats)
Out[22]:
array([False,  True,  True], dtype=bool)

So the above boolean index needs to be applied to the last 3 rows rather to the entire df again which is what you are doing