如果值在另一列中，则来自另一个DataFrame的pandas列? [英] pandas columns from another DataFrame if value is in another column?

问题描述

我有pd.DataFrame列出了线规及其相应的电流:

I have pd.DataFrame listing wire gauges and their corresponding currents:

e_ref =

   wire_gauge  current
0          14       15
1          12       20
2          10       30
3           8       50
4           6       60
5           4       85
6           3      100
7           2      115

另一个DataFrame列出了系统中的断路器:

Another DataFrame lists breakers in a system:

system =

    breakers
0         30
1         20
2         30
3         15
4         30

我需要通过查找e_ref当前序列中的断路器值，从e_ref数据框架的"wire_gauge"列中向系统DataFrame添加一个线规"列.

I need to add a "wire gauge" column to the system DataFrame from the "wire_gauge" columns of the e_ref DataFrame by looking up the breaker value in the current series of the e_ref.

所以输出将是:

    breakers  wire_gauge
0         30  10
1         20  12
2         30  10
3         15  14
4         30  10

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我一直在混淆其他帖子中的几个答案，并且目前没有有效的熊猫解决方案.我可以使用python循环使它正常工作，但是我觉得这里有一只熊猫内胆...

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I keep confusing several answers from other post and currently do not have a working pandas solution. I can get this working using python loops but I feel like there is a pandas one liner here...

以下是我正在研究的解决方案类型:

Below are the types of solutions I'm working on:

df.ix[df.breakers.isin(e_ref['current']), 'wire_gauge'] = e_ref['wire_gauge']

和

df['wire_gauge']=e_ref.loc[e_ref['current'] == df['breakers'] ]

感谢您的时间和方向！

推荐答案

使用Series创建的e_ref或 map . join.html"rel =" nofollow noreferrer> join ，但e_ref中current列中的必要值必须唯一:

Use map by Series created form e_ref or join, but is necessary values in currentcolumn in e_ref has to be unique:

print (e_ref['current'].is_unique)
True

s = e_ref.set_index('current')['wire_gauge']
system['wire_gauge'] = system['breakers'].map(s)
print (system)
   breakers  wire_gauge
0        30          10
1        20          12
2        30          10
3        15          14
4        30          10

替代:

df = system.join(e_ref.set_index('current'), on='breakers')
print (df)
   breakers  wire_gauge
0        30          10
1        20          12
2        30          10
3        15          14
4        30          10

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