combine/merge two csv using pandas/python

Question

I have two csvs, I want to combine or merge these csvs as left join... my key column is "id", I have same non-key column as "result" in both csvs, but I want to override "result" column if any value exists in "result" column of 2nd CSV . How can I achieve that using pandas or any scripting lang. Please see my final expected output.

Input

input.csv:

id,scenario,data1,data2,result
1,s1,300,400,"{s1,not added}"
2,s2,500,101,"{s2 added}"
3,s3,600,202,

output.csv:

id,result
1,"{s1,added}"
3,"{s3,added}"

Expected Output

final_output.csv

id,scenario,data1,data2,result
1,s1,300,400,"{s1,added}"
2,s2,500,101,"{s2 added}"
3,s3,600,202,"{s3,added}"

Current Code:

import pandas as pd

a = pd.read_csv("input.csv")
b = pd.read_csv("output.csv")
merged = a.merge(b, on='test_id',how='left')
merged.to_csv("final_output.csv", index=False)

Question:

Using this code I am getting the result column twice. I want only once and it should override if value exists in that column. How do I get a single result column?

Answer 1

try this, this works as well

import pandas as pd
import numpy as np
c=pd.merge(a,b,on='id',how='left')
lst=[]
for i in c.index:
    if(c.iloc[i]['result_x']!=''):
         lst.append(c.iloc[i]['result_x'])
    else:
         lst.append(c.iloc[i]['result_y'])
c['result']=pd.Series(lst)
del c['result_x']
del c['result_y']

Answer 2

This will combine the columns as desired:

import pandas as pd

a = pd.read_csv("input.csv")
b = pd.read_csv("output.csv")
merged = a.merge(b, on='id', how='outer')

def merge_results(row):
    y = row['result_y']
    return row['result_x'] if isinstance(y, float) else y

merged['result'] = merged.apply(merge_results, axis=1)
del merged['result_x']
del merged['result_y']

merged.to_csv("final_output.csv", index=False)