How to sort pandas dataframe in a special way

Question

Given a pandas dataframe

df = pd.DataFrame({'a': [1,2,3,4,5,6,7,8],
                   'b': [0,0,1,1,2,2,3,3]})

How to sort it along the column b in such a way that it is rearranged as {0,1,2,3,0,1,2,3}.

I.e. the resulting dataframe is

1   0
3   1
5   2
7   3
2   0
4   1
6   2
8   3

Answer 1

Add a column using cumcount

df.assign(x=df.groupby('b').cumcount()).sort_values(['x', 'b']).drop('x', axis=1)

   a  b
0  1  0
2  3  1
4  5  2
6  7  3
1  2  0
3  4  1
5  6  2
7  8  3

---

Numpy's lexsort, iloc, and cumcount

df.iloc[np.lexsort([df['b'], df.groupby('b').cumcount()])]

   a  b
0  1  0
2  3  1
4  5  2
6  7  3
1  2  0
3  4  1
5  6  2
7  8  3