Question

像这样的数据框，我正在添加映射和计算中的一些列。

   code month of entry   name  reports
0    JJ       20171002  Jason       14
1    MM       20171206  Molly       24
2    TT       20171208   Tina       31
3    JJ       20171018   Jake       22
4    AA       20090506    Amy       34
5    DD       20171128  Daisy       16
6    RR       20101216  River       47
7    KK       20171230   Kate       32
8    DD       20171115  David       14
9    JJ       20171030   Jack       10
10   NN       20171216  Nancy       28

它在这里做的是选择一些行并从字典中查找值并从简单计算中插入另一列。它工作正常：

import pandas as pd

data = {'name': ['Jason', 'Molly', 'Tina', 'Jake', 'Amy', 'Daisy', 'River', 'Kate', 'David', 'Jack', 'Nancy'], 
    'code' : ['JJ', 'MM', 'TT', 'JJ', 'AA', 'DD', 'RR', 'KK', 'DD', 'JJ', 'NN'],
    'month of entry': ["20171002", "20171206", "20171208", "20171018", "20090506", "20171128", "20101216", "20171230", "20171115", "20171030", "20171216"],
    'reports': [14, 24, 31, 22, 34, 16, 47, 32, 14, 10, 28]}
df = pd.DataFrame(data)

dict_hour = {'JasonJJ' : 3, 'MollyMM' : 6, 'TinaTT' : 2, 'JakeJJ' : 3, 'AmyAA' : 8, 'DaisyDD' : 6, 'RiverRR' : 4, 'KateKK' : 8, 'DavidDD' : 5, 'JackJJ' : 5, 'NancyNN' : 2}

wanted = ['JasonJJ', 'TinaTT', 'AmyAA', 'DaisyDD', 'KateKK']

df['name_code'] = df['name'].astype(str) + df['code'].astype(str)

df1 = df[df['name_code'].isin(wanted)]

df1['hour'] = df1['name_code'].map(dict_hour).astype(float)

df1['coefficient'] = df1['reports'] / df1['hour'] - 1

但是最后两行收到了同样的警告：

SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead

如何相应地改进代码？谢谢。

Answer 1

您需要copy：

df1 = df[df['name_code'].isin(wanted)].copy()

如果稍后修改df1中的值，您会发现修改不会传播回原始数据（df），并且Pandas会发出警告。

Python，Pandas从计算中添加列

1 个答案: