error.txt

/export/home/ccprakt3/miniconda3/lib/python3.9/site-packages/pandas/core/frame.py:3607: SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead

See the caveats in the documentation: https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy
  self._set_item(key, value)

loc.py

rows = [{'a': 1, 'b': 2}, {'a':3, 'b':4}]
df = pd.DataFrame(rows)
df = df.set_index(['mutant', 'method', 'state id', 'transition id'])
df.sort_index(level=['mutant','method', 'state id', 'transition id'], inplace=True)
orb_map = np.loadtxt('../F/BLYP-B3LYP-orbital-overlap.txt', skiprows=1)
df1 = df.loc[("NH2", "BLYP"), :]
df2 = df.loc[("NH2", "B3LYP"), :]

df1.loc[:, "mapped occupied"] =  df1.loc[:,"occupied"].map(lambda o: int(orb_map[orb_map == o][1]))