Python从另一个csv追加新列

Question

I generate every days a csv (overwrited) with this two columns(have not headers). First is client number and second is the daily sells

963840      3
18065729    2
255657800   4
338082549   183
364915832   2
392633366   14
450647013   3

I need to append in a new csv the daily sells, each day on a new column to know the evolution

963840      3       5     6    20
18065729    2       4     7     8   
255657800   4       7
338082549   183     220
364915832   2       5
392633366   14      14
450647013   3       4

thanks in advance

Answer 1

I tried to write it symbolic so you can follow the code and load your CSV files and merge them:

basedf = pd.read_csv('firstday.csv')

days = ['day2.csv','day3.csv','day4.csv','day5.csv']
for day in days:
    df = pd.read_csv(day)
    basedf = basedf.merge(df,on='clientid',how='left')

Answer 2

Maybe outer join works better if you have different customers in different days.

import pandas as pd
day1 = pd.DataFrame({'id': ['963840', '18065729', '255657800', '338082549','364915832','392633366','450647013'],
                    'day1data': [3,2,4,183,2,14,3]})
day2 = pd.DataFrame({'id': ['963840', '18065729', '255657800', '338082549','364915832','392633366','450647013'],
                    'day2data': [5,4,7,220,5,14,4]})

print(day1.merge(day2, on='id', how='outer'))

Ant the result will be as below:

          id  day1data  day2data
0     963840         3         5
1   18065729         2         4
2  255657800         4         7
3  338082549       183       220
4  364915832         2         5
5  392633366        14        14
6  450647013         3         4

Also if you want to save as csv, you can use to_csv() method.

day1.merge(day2, on='id', how='outer').to_csv('merged_data.csv',sep=';')