python - Merge two dataframe in pandas

Question

I am merging two csv(data frame) using below code:

import pandas as pd
a = pd.read_csv(file1,dtype={'student_id': str})
df = pd.read_csv(file2)
c=pd.merge(a,df,on='test_id',how='left')
c.to_csv('test1.csv', index=False)

I have the following CSV files

file1:

test_id, student_id
1, 01990
2, 02300
3, 05555

file2:

test_id, result
1, pass
3, fail

after merge

test_id, student_id , result
1, 1990, pass
2, 2300,
3, 5555, fail

If you notice student_id has 0 appended at the beginning and it's supposed to be considered as text but after merging and using to_csv function it converts it into numeric and removes leading 0.

How can I keep the column as "text" even after to_csv?

I think its to_csv function which saves back again as numeric Added dtype={'student_id': str} while reading csv.. but while saving it as to_csv .. it again convert it to numeric

Answer 1

Caveat Please use merge or join. This answer is provided to give perspective on the flexibility pandas gives you and how many different ways there are to answer the same question.

a = pd.read_csv('file1.csv', converters=dict(student_id=str), skipinitialspace=True)
df = pd.read_csv('file2.csv')
results = pd.concat(
    [d.set_index('test_id') for d in [a, df]],
    axis=1, join='outer'
).reset_index()