pandas 按新的日期范围重新索引数据框
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Re-index dataframe by new range of dates
提问by Gianluca
I have a data frame containing a number of observations:
我有一个包含许多观察结果的数据框：
date colour orders
2014-10-20 red 7
2014-10-21 red 10
2014-10-20 yellow 3
I would like to re-index the data frame and standardise the dates.
我想重新索引数据框并标准化日期。
date colour orders
2014-10-20 red 7
2014-10-21 red 10
2014-10-22 red NaN
2014-10-20 yellow 3
2014-10-21 yellow NaN
2014-10-22 yellow NaN
I though to order the data frame by colourand date, and then try to re-index it.
我想通过colour和对数据框进行排序date，然后尝试重新索引它。
index = pd.date_range('20/10/2014', '22/10/2014')
test_df = df.sort(['colour', 'date'], ascending=(True, True))
ts = test_df.reindex(index)
ts
But it returns a new data frame with the right index but all NaNvalues.
但它返回一个具有正确索引但所有NaN值的新数据框。
date colour orders
2014-10-20 NaN NaN
2014-10-21 NaN NaN
2014-10-22 NaN NaN
回答by joris
Starting from your exampe dataframe:
从您的示例数据框开始：
In [51]: df
Out[51]:
date colour orders
0 2014-10-20 red 7
1 2014-10-21 red 10
2 2014-10-20 yellow 3
If you want to reindex on both 'date' and 'colour', one possibility is to set both as the index (a multi-index):
如果要重新索引“日期”和“颜色”，一种可能性是将两者都设置为索引（多索引）：
In [52]: df = df.set_index(['date', 'colour'])
In [53]: df
Out[53]:
orders
date colour
2014-10-20 red 7
2014-10-21 red 10
2014-10-20 yellow 3
You can now reindex this dataframe, after you constructed to desired index:
在构建到所需的索引后，您现在可以重新索引此数据框：
In [54]: index = pd.date_range('20/10/2014', '22/10/2014')
In [55]: multi_index = pd.MultiIndex.from_product([index, ['red', 'yellow']])
In [56]: df.reindex(multi_index)
Out[56]:
orders
2014-10-20 red 7
yellow 3
2014-10-21 red 10
yellow NaN
2014-10-22 red NaN
yellow NaN
To have the same output as your example output, the index should be sorted in the second level (level=1as it is 0-based):
要获得与示例输出相同的输出，索引应在第二级排序（level=1因为它是基于 0 的）：
In [60]: df2 = df.reindex(multi_index)
In [64]: df2.sortlevel(level=1)
Out[64]:
orders
2014-10-20 red 7
2014-10-21 red 10
2014-10-22 red NaN
2014-10-20 yellow 3
2014-10-21 yellow NaN
2014-10-22 yellow NaN
A possible way to generate the multi-index automatically would be (with your original frame):
自动生成多索引的一种可能方法是（使用您的原始框架）：
pd.MultiIndex.from_product([pd.date_range(df['date'].min(), df['date'].max(), freq='D'),
df['colour'].unique()])
Another waywould be to use resamplefor each group of colors:
另一种方法是resample用于每组颜色：
In [77]: df = df.set_index('date')
In [78]: df.groupby('colour').resample('D')
This is simpler, but this does not give you the full range of dates for each colour, only the range of dates that is available for that colour group.
这更简单，但这不会为您提供每种颜色的完整日期范围，只会提供该颜色组可用的日期范围。
