pandas 从两个列表中获取元素的所有组合？
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Get all combinations of elements from two lists?
提问by K.Chen
If I have two lists
如果我有两个列表
l1 = [ 'A', 'B' ]
l2 = [ 1, 2 ]
what is the most elegant way to get a pandas data frame which looks like:
获取如下所示的 Pandas 数据框的最优雅方法是什么：
+-----+-----+-----+
| | l1 | l2 |
+-----+-----+-----+
| 0 | A | 1 |
+-----+-----+-----+
| 1 | A | 2 |
+-----+-----+-----+
| 2 | B | 1 |
+-----+-----+-----+
| 3 | B | 2 |
+-----+-----+-----+
Note, the first column is the index.
请注意，第一列是索引。
回答by behzad.nouri
回答by Andy Hayden
As an alternative you can use pandas' cartesian_product(may be more useful with large numpy arrays):
作为替代方案，您可以使用 pandas' cartesian_product（对于大型 numpy 数组可能更有用）：
In [11]: lp1, lp2 = pd.core.reshape.util.cartesian_product([l1, l2])
In [12]: pd.DataFrame(dict(l1=lp1, l2=lp2))
Out[12]:
l1 l2
0 A 1
1 A 2
2 B 1
3 B 2
This seems a little messy to read in to a DataFrame with the correct orient...
以正确的方向读入 DataFrame 似乎有点混乱......
Note: previously cartesian_productwas located at pd.tools.util.cartesian_product.
注意：以前cartesian_product位于pd.tools.util.cartesian_product.
回答by jpp
You can also use the sklearnlibrary, which uses a NumPy-based approach:
您还可以使用sklearn使用基于 NumPy 的方法的库：
from sklearn.utils.extmath import cartesian
df = pd.DataFrame(cartesian((L1, L2)))
For more verbose but possibly more efficient variants see Numpy: cartesian product of x and y array points into single array of 2D points.
有关更详细但可能更有效的变体，请参阅Numpy: cartesian product of x and y array points into single array of 2D points。
