[英]How to update a column in Pandas Dataframe
在Pandas
,我尝试使用来自另一个数据框(DF1)的值向数据框(DF2)添加新列/更新现有列。 我可以想到如何在SQL
执行此操作
UPDATE DF2
SET DF2['Column'] = DF1['Column']
FROM DF2
JOIN DF1 ON DF1['NonIndexColumn'] = DF2['NonIndexColumn']
数据示例:
d =[{'CustomerID': 1, 'SignUpDate': '2014-01-01'}, {'CustomerID': 2, 'SignUpDate': '2014-02-01'}, {'CustomerID': 3, 'SignUpDate': '2014-03-01'}, {'CustomerID': 4, 'SignUpDate': '2014-04-01'}]
DF1 = pd.DataFrame(data=d)
d2 = [{'OrderID': 1, 'CustomerID': 1, 'OrderDate': '2014-01-15'}, {'OrderID': 2, 'CustomerID': 1, 'OrderDate': '2014-01-15'}, {'OrderID': 3, 'CustomerID': 2, 'OrderDate': '2014-03-28'}, {'OrderID': 4, 'CustomerID': 1, 'OrderDate': '2014-03-29'}, {'OrderID': 5, 'CustomerID': 3, 'OrderDate': '2014-04-28'}, {'OrderID': 6, 'CustomerID': 2, 'OrderDate': '2014-06-01'}, {'OrderID': 7, 'CustomerID': 1, 'OrderDate': '2014-11-06'}, {'OrderID': 8, 'CustomerID': 3, 'OrderDate': '2015-01-28'}, {'OrderID': 9, 'CustomerID': 1, 'OrderDate': '2015-02-15'} ]
DF2 = pd.DataFrame(data=d2)
我试图将DF1['SignUpDate']
添加到DF2
,以便DF2
看起来像这样:
CustomerID OrderDate OrderID SignUpDate
0 1 2014-01-15 1 2014-01-01
1 1 2014-01-15 2 2014-01-01
2 2 2014-03-28 3 2014-02-01
3 1 2014-03-29 4 2014-01-01
4 3 2014-04-28 5 2014-03-01
5 2 2014-06-01 6 2014-02-01
6 1 2014-11-06 7 2014-01-01
7 3 2015-01-28 8 2014-03-01
8 1 2015-02-15 9 2014-01-01
我知道merge
将使我能够添加列,但是我将不得不覆盖现有DF或创建一个新的DF,如下所示:
DF1 = pd.merge(DF1, DF2) #overwrite
DF3 = pd.merge(DF1, DF2) #new dataframe
有没有一种方法可以在一个字段上联接(可能是索引列,也可能不是索引列)并更新/添加字段?
执行左merge
:
In [4]:
DF2.merge(DF1, on='CustomerID', how='left')
Out[4]:
CustomerID OrderDate OrderID SignUpDate
0 1 2014-01-15 1 2014-01-01
1 1 2014-01-15 2 2014-01-01
2 2 2014-03-28 3 2014-02-01
3 1 2014-03-29 4 2014-01-01
4 3 2014-04-28 5 2014-03-01
5 2 2014-06-01 6 2014-02-01
6 1 2014-11-06 7 2014-01-01
7 3 2015-01-28 8 2014-03-01
8 1 2015-02-15 9 2014-01-01
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