How to vlookup within a single dataframe?

Question content

comes from the following data frame (df):

|------------+--------------------+-------------|
| child_code | child_name         | parent_code |
|------------+--------------------+-------------|
|        900 | world              |           0 |
|        920 | south-eastern asia |         900 |
|        702 | singapore          |         920 |
|------------+--------------------+-------------|

I want to generate this data frame:

|------------+--------------------+-------------+--------------------|
| child_code | child_name         | parent_code | parent_name        |
|------------+--------------------+-------------+--------------------|
|        900 | World              |           0 |                    |
|        920 | South-Eastern Asia |         900 | World              |
|        702 | Singapore          |         920 | South-Eastern Asia |
|------------+--------------------+-------------+--------------------|```
How could I make the equivalent of an MS Excel `vlookup` to produce the `parent_name` column?

Correct answer

You can use series.map:

import pandas as pd
import numpy as np

data = {'child_name': {0: 'World', 1: 'South-Eastern Asia', 2: 'Singapore'}, 
        'child_code': {0: 900, 1: 920, 2: 702}, 
        'parent_code': {0: 0, 1: 900, 2: 920}}
df = pd.DataFrame(data)

df['parent_name'] = df['parent_code'].map(df.set_index('child_code')['child_name'])

df

           child_name  child_code  parent_code         parent_name
0               World         900            0                 NaN
1  South-Eastern Asia         920          900               World
2           Singapore         702          920  South-Eastern Asia

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