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[英]find a value in a dataframe and add precedent column value in a new column in pandas
[英]Find the minimum value in a Pandas dataframe and add a label on new column
我可以对我的 python pandas 代码进行哪些改进以提高效率? 就我而言,我有这个 dataframe
In [1]: df = pd.DataFrame({'PersonID': [1, 1, 1, 2, 2, 2, 3, 3, 3],
'Name': ["Jan", "Jan", "Jan", "Don", "Don", "Don", "Joe", "Joe", "Joe"],
'Label': ["REL", "REL", "REL", "REL", "REL", "REL", "REL", "REL", "REL"],
'RuleID': [55, 55, 55, 3, 3, 3, 10, 10, 10],
'RuleNumber': [3, 4, 5, 1, 2, 3, 234, 567, 999]})
这给出了这个结果:
In [2]: df
Out[2]:
PersonID Name Label RuleID RuleNumber
0 1 Jan REL 55 3
1 1 Jan REL 55 4
2 1 Jan REL 55 5
3 2 Don REL 3 1
4 2 Don REL 3 2
5 2 Don REL 3 3
6 3 Joe REL 10 234
7 3 Joe REL 10 567
8 3 Joe REL 10 999
我需要在这里完成的是将 Label 列下的字段更新为 MAIN,以获取与应用于人员 ID 和名称的每个规则 ID 关联的最低规则值。 因此,结果需要如下所示:
In [3]: df
Out[3]:
PersonID Name Label RuleID RuleNumber
0 1 Jan MAIN 55 3
1 1 Jan REL 55 4
2 1 Jan REL 55 5
3 2 Don MAIN 3 1
4 2 Don REL 3 2
5 2 Don REL 3 3
6 3 Joe MAIN 10 234
7 3 Joe REL 10 567
8 3 Joe REL 10 999
这是我为实现此目的而编写的代码:
In [4]:
df['Label'] = np.where(
df['RuleNumber'] ==
df.groupby(['PersonID', 'Name', 'RuleID'])['RuleNumber'].transform('min'),
"MAIN", df.Label)
有没有更好的方法来更新 Label 列下的值? 我觉得我是蛮横的,这可能不是最有效的方法。
我使用以下 SO 线程得出我的结果:
https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.idxmin.html
https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.transform.html
任何意见,将不胜感激。
谢谢你。
似乎您可以按分组的idxmin
进行过滤,而不管排序顺序如何,并以此为基础更新RuleNumber
。 您可以使用loc
、 np.where
、 mask
或where
,如下所示:
df.loc[df.groupby(['PersonID', 'Name', 'RuleID'])['RuleNumber'].idxmin(), 'Label'] = 'MAIN'
或与np.where
一起尝试:
df['Label'] = (np.where((df.index == df.groupby(['PersonID', 'Name', 'RuleID'])
['RuleNumber'].transform('idxmin')), 'MAIN', 'REL'))
df
Out[1]:
PersonID Name Label RuleID RuleNumber
0 1 Jan MAIN 55 3
1 1 Jan REL 55 4
2 1 Jan REL 55 5
3 2 Don MAIN 3 1
4 2 Don REL 3 2
5 2 Don REL 3 3
6 3 Joe MAIN 10 234
7 3 Joe REL 10 567
8 3 Joe REL 10 999
使用mask
或其反函数where
也可以:
df['Label'] = (df['Label'].mask((df.index == df.groupby(['PersonID', 'Name', 'RuleID'])
['RuleNumber'].transform('idxmin')), 'MAIN'))
或者
df['Label'] = (df['Label'].where((df.index != df.groupby(['PersonID', 'Name', 'RuleID'])
['RuleNumber'].transform('idxmin')), 'MAIN'))
import pandas as pd
df = pd.DataFrame({'PersonID': [1, 1, 1, 2, 2, 2, 3, 3, 3],
'Name': ["Jan", "Jan", "Jan", "Don", "Don", "Don", "Joe", "Joe", "Joe"],
'Label': ["REL", "REL", "REL", "REL", "REL", "REL", "REL", "REL", "REL"],
'RuleID': [55, 55, 55, 3, 3, 3, 10, 10, 10],
'RuleNumber': [3, 4, 5, 1, 2, 3, 234, 567, 999]})
df.loc[df.groupby('Name')['RuleNumber'].idxmin()[:], 'Label'] = 'MAIN'
在 PersonID 上使用duplicated
:
df.loc[~df['PersonID'].duplicated(),'Label'] = 'MAIN'
print(df)
Output:
PersonID Name Label RuleID RuleNumber
0 1 Jan MAIN 55 3
1 1 Jan REL 55 4
2 1 Jan REL 55 5
3 2 Don MAIN 3 1
4 2 Don REL 3 2
5 2 Don REL 3 3
6 3 Joe MAIN 10 234
7 3 Joe REL 10 567
8 3 Joe REL 10 999
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