pandas.DataFrame.unstack¶
DataFrame.unstack(level=- 1, fill_value=None)[source]-
Pivot a level of the (necessarily hierarchical) index labels.
Returns a DataFrame having a new level of column labels whose inner-most level consists of the pivoted index labels.
If the index is not a MultiIndex, the output will be a Series (the analogue of stack when the columns are not a MultiIndex).
- Parameters
- levelint, str, or list of these, default -1 (last level)
-
Level(s) of index to unstack, can pass level name.
- fill_valueint, str or dict
-
Replace NaN with this value if the unstack produces missing values.
- Returns
- Series or DataFrame
这是一个有意思的方法，实在很有意思。unstack，当dataframe对象是有一个多层index的时候，会从index中抽出去，填补到columns中去，
如果一个多层index的Series，就会变成了DataFrame对象。
如果是一个单层的index的DataFrame对象，[如果列的索引是多层索引],则会返回一个Series对象，列索引变成行索引的多层索引的第一层。
Example
index = pd.MultiIndex.from_tuples([('one', 'a'), ('one', 'b'),
('two', 'a'), ('two', 'b')])
s = pd.Series(np.arange(1.0, 5.0), index=index)
s
one a 1.0
b 2.0
two a 3.0
b 4.0
dtype: float64
In [12]: s
Out[12]:
one a 1.0
b 2.0
two a 3.0
b 4.0
dtype: float64
In [13]: s.unstack()
Out[13]:
a b
one 1.0 2.0
two 3.0 4.0
In [14]: s.unstack(-1)
Out[14]:
a b
one 1.0 2.0
two 3.0 4.0
In [15]: s.unstack(0)
Out[15]:
one two
a 1.0 3.0
b 2.0 4.0