从 pandas 内部获取上一行值apply()函数

本文介绍了从 pandas 内部获取上一行值apply()函数的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 import pandas as pd def greater_or_less(d): if d['current'] > d['previous']: d['result']="Greater" elif d['current'] < d['previous']: d['result']="Less" elif d['current'] == d['previous']: d['result']="Equal" else: pass return d df=pd.DataFrame({'current':[1,2,2,8,7]}) # Duplicate the column with shifted values df['previous']=df['current'].shift(1) df['result']="" df=df.apply(greater_or_less,axis=1)

结果是:

current previous result 1 NaN 2 1 Greater 2 2 Equal 8 2 Greater 7 8 Less

然后我将删除previous列，因为它不再需要了.结束于:

I'd then drop the previous column as it's no longer needed. Ending up with:

current result 1 2 Greater 2 Equal 8 Greater 7 Less

如何在不添加额外列的情况下执行此操作?

How can I do this without adding the extra column?

我想做的是知道如何从greater_or_less函数中引用上一行的值.

What i'd like to do, is know how to reference the previous row's value from within the greater_or_less function.

推荐答案

使用diff()方法:

import pandas as pd import numpy as np df=pd.DataFrame({'current':[1,2,2,8,7]}) np.sign(df.current.diff()).map({1:"Greater", 0:"Equal", -1:"Less"})