Question

早上好，我有以下df：

print(df)

Date          cod_id      Sales    Initial_stock  
01/01/2017      1           5          5                
01/01/2017      2           4          8                
02/01/2017      1           1          5                 
...

由于真实数据集中存在一些错误，关于“Initial_stock”，我想为不同的 cod_id s（=产品）创建一个新列，如下：

cod_id 前一行的初始库存+初始库存的当前值 - 销售额;这样：

print(df_final)

Date          cod_id      Sales    Initial_stock  new  
01/01/2017      1           5          5           0          
01/01/2017      2           4          8           4                      
02/01/2017      1           1          5           4  
...

其中最后一个值等于4的“cod_id 1”计算如下：0 + 5 - 1 = 4

Answer 1

import pandas as pd
from pandas import DataFrame

d = {'cod_id': [1, 2, 1], 'Sales': [5,4,1], 'Initial_stock': [5,8,5]}#my initil data

#######show purpose#######
df = pd.DataFrame(data=d)#I print the dataframe of my initial data
print (df)
##########################

new=[]#declare a new list where I'll introduce all the new values
i=0
#I create a loop for element present in my initial list and for each subelement present I calculate the new one
while i <len(d['cod_id']):
    new_value=(d['Initial_stock'][i])-(d['Sales'][i])#clculation new=initial_stock-sales
    new.append(new_value)#append my new value in the new list
    i+=1

#######show purpose#######
print (new)#print my new list to show that the calculation is correct
##########################

d['new']=new#add my new data to the original list

#######show purpose#######
df = pd.DataFrame(data=d)#create the data frame with my new values and print it again
print (df)
##########################

分组并总结前一个元素

1 个答案: