Pandas:填充缺失日期的数据 [英] Pandas: Filling data for missing dates
问题描述
假设我有下表:
ProdID Date Val1 Val2 Val3
Prod1 4/1/2019 1 3 4
Prod1 4/3/2019 2 3 54
Prod1 4/4/2019 3 4 54
Prod2 4/1/2019 1 3 3
Prod2 4/2/2019 1 3 4
Prod2 4/3/2019 2 4 4
Prod2 4/4/2019 2 5 3
Prod2
条目已正确填充,因为我们获得了从 4/1/2019
到 4/4/2019
的数据.
Prod2
entries are populated correctly as we've got the data from 4/1/2019
to 4/4/2019
.
Prod1
缺少 1 个日期 - 4/2/2019
.
Prod1
has 1 missing date - 4/2/2019
.
我想找到所有 ProdID 的缺失日期,并用从上一个条目的最后一个复制的数据填充 Val1-3.例如,我想将数据从 4/1/2019
复制到 4/2/2019
I would like to find missing dates for all ProdIDs and fill in Val1-3 with data copied from the last of previous entry. For instance, I would like to copy data from 4/1/2019
to 4/2/2019
ProdID Date Val1 Val2 Val3
Prod1 4/1/2019 1 3 4
Prod1 4/2/2019 1 3 4
Prod1 4/3/2019 2 3 54
Prod1 4/4/2019 3 4 54
Prod2 4/1/2019 1 3 3
Prod2 4/2/2019 1 3 4
Prod2 4/3/2019 2 4 4
Prod2 4/4/2019 2 5 3
推荐答案
First convert column to datetime
s by to_datetime
,然后通过 DataFrame.set_index
并调用 GroupBy.apply
与 DataFrame.asfreq
- 也可以指定向前或向后填充缺失值的方法:
First convert column to datetime
s by to_datetime
, then create DatetimeIndex
by DataFrame.set_index
and call GroupBy.apply
with DataFrame.asfreq
- there is also possible specify method for forward or back filling missing values:
df['Date'] = pd.to_datetime(df['Date'])
df1 = (df.set_index('Date')
.groupby('ProdID')
.apply(lambda x: x.asfreq('D', method='ffill'))
.reset_index(level=0, drop=True)
.reset_index()
.reindex(df.columns, axis=1))
print (df1)
ProdID Date Val1 Val2 Val3
0 Prod1 2019-04-01 1 3 4
1 Prod1 2019-04-02 1 3 4
2 Prod1 2019-04-03 2 3 54
3 Prod1 2019-04-04 3 4 54
4 Prod2 2019-04-01 1 3 3
5 Prod2 2019-04-02 1 3 4
6 Prod2 2019-04-03 2 4 4
7 Prod2 2019-04-04 2 5 3
另一种解决方案是通过 datetimes 的所有组合"nofollow noreferrer">product
和 DataFrame.merge
使用左连接,最后通过 ffill
向前填充缺失值:
Another solution is create all combinations of product and datetimes
by product
and DataFrame.merge
with left join, last forward filling missing values by ffill
:
dates = pd.date_range(start=df['Date'].min(), end=df['Date'].max())
prods = df.ProdID.unique()
from itertools import product
df1 = pd.DataFrame(list(product(prods, dates)), columns=['ProdID', 'Date'])
print (df1)
ProdID Date
0 Prod1 2019-04-01
1 Prod1 2019-04-02
2 Prod1 2019-04-03
3 Prod1 2019-04-04
4 Prod2 2019-04-01
5 Prod2 2019-04-02
6 Prod2 2019-04-03
7 Prod2 2019-04-04
df = df1.merge(df, how='left').ffill()
print (df)
ProdID Date Val1 Val2 Val3
0 Prod1 2019-04-01 1.0 3.0 4.0
1 Prod1 2019-04-02 1.0 3.0 4.0
2 Prod1 2019-04-03 2.0 3.0 54.0
3 Prod1 2019-04-04 3.0 4.0 54.0
4 Prod2 2019-04-01 1.0 3.0 3.0
5 Prod2 2019-04-02 1.0 3.0 4.0
6 Prod2 2019-04-03 2.0 4.0 4.0
7 Prod2 2019-04-04 2.0 5.0 3.0
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