当在应用中也计算前一个值时，Pandas 中是否可以使用 dataframe.apply 中的前一行值?

2022-01-24 00:00:00 python pandas dataframe iteration for-loop

问题描述

我有以下数据框:

 Index_Date    A    B    C    D
 ===============================
 2015-01-31    10   10   Nan  10
 2015-02-01     2    3   Nan  22 
 2015-02-02    10   60   Nan  280
 2015-02-03    10   100   Nan  250

要求:

 Index_Date    A    B    C    D
 ===============================
 2015-01-31    10   10   10   10
 2015-02-01     2    3   23   22
 2015-02-02    10   60   290  280
 2015-02-03    10   100  3000 250

Column C 是通过取 D 的 value 为 2015-01-31 派生的.

Column C is derived for 2015-01-31 by taking value of D.

那我需要将C的value用于2015-01-31并乘以value A 在 2015-02-01 并添加 B.

Then I need to use the value of C for 2015-01-31 and multiply by the value of A on 2015-02-01 and add B.

我尝试了一个 apply 和一个 shift 使用一个 if else 这给出了一个关键错误.

I have attempted an apply and a shift using an if else by this gives a key error.

解决方案

首先，创建派生值:

df.loc[0, 'C'] = df.loc[0, 'D']

然后遍历剩余的行并填充计算值:

Then iterate through the remaining rows and fill the calculated values:

for i in range(1, len(df)): df.loc[i, 'C'] = df.loc[i-1, 'C'] * df.loc[i, 'A'] + df.loc[i, 'B'] Index_Date A B C D 0 2015-01-31 10 10 10 10 1 2015-02-01 2 3 23 22 2 2015-02-02 10 60 290 280

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