Pandas: drop a level from a multi-level column index?
You can use MultiIndex.droplevel
:
>>> cols = pd.MultiIndex.from_tuples([("a", "b"), ("a", "c")])>>> df = pd.DataFrame([[1,2], [3,4]], columns=cols)>>> df a b c0 1 21 3 4[2 rows x 2 columns]>>> df.columns = df.columns.droplevel()>>> df b c0 1 21 3 4[2 rows x 2 columns]
Another way to drop the index is to use a list comprehension:
df.columns = [col[1] for col in df.columns] b c0 1 21 3 4
This strategy is also useful if you want to combine the names from both levels like in the example below where the bottom level contains two 'y's:
cols = pd.MultiIndex.from_tuples([("A", "x"), ("A", "y"), ("B", "y")])df = pd.DataFrame([[1,2, 8 ], [3,4, 9]], columns=cols) A B x y y0 1 2 81 3 4 9
Dropping the top level would leave two columns with the index 'y'. That can be avoided by joining the names with the list comprehension.
df.columns = ['_'.join(col) for col in df.columns] A_x A_y B_y0 1 2 81 3 4 9
That's a problem I had after doing a groupby and it took a while to find this other question that solved it. I adapted that solution to the specific case here.
As of Pandas 0.24.0, we can now use DataFrame.droplevel():
cols = pd.MultiIndex.from_tuples([("a", "b"), ("a", "c")])df = pd.DataFrame([[1,2], [3,4]], columns=cols)df.droplevel(0, axis=1) # b c#0 1 2#1 3 4
This is very useful if you want to keep your DataFrame method-chain rolling.