当应用中也计算了先前的值时，Pandas 是否有办法在 dataframe.apply 中使用先前的行值? [英] Is there a way in Pandas to use previous row value in dataframe.apply when previous value is also calculated in the apply?

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 导出的.

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

然后我需要将C的value用于2015-01-31并乘以value> 在 2015-02-01 上的 A 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 if else 这会导致一个关键错误.

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

推荐答案

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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