How do I take data from one csv file and find the results in another using python?


I have two csv files with data in both of them. The first one has columns of data like the following:
CSV File

And the second csv file looks like this
CSV File2

What I want to do is able to group these together based on the values in column D. I want to create a new column next to D that matches its value to the detail in the second file. The output would look something like:

File number 1 is always changing numbers and there are hundreds of numbers in each file so I don’t want to write them manually in a list for the code.

Asked By: a_44



Use Pandas:

import pandas as pd

df1 = pd.read_csv('first_file.csv')
df2 = pd.read_csv('second_file.csv')

df1['Details'] = df1['D'].map(df2.set_index('Number')['Details'])
# or
df1 = df1.merge(df2, left_on='D', right_on='Number', how='left')

df1.to_excel('merge_file.csv', index=False)

Update: the same version with csv module:

import csv

with (open('first_file.csv') as fp1,
      open('second_file.csv') as fp2,
      open('merge_file.csv', 'w') as out):
    df1 = csv.DictReader(fp1)
    df2 = csv.DictReader(fp2)
    mapping = {row['Number']: row['Details'] for row in df2}
    dfm = csv.DictWriter(out, df1.fieldnames + ['Details'])
    for row in df1:
        dfm.writerow(dict(row, Details=mapping.get(row['D'], '')))


A B C D Details
15 22 13 41 comma
52 36 67 87 carrer
91 150 41 12 recording
123 14 76 16 mold
Answered By: Corralien
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