Python - reorder pandas Dataframe rows based on column values

Question

I have a dataframe with 2 columns : id , antecedent_id I would like a code to reorder the dataframe in the right order using antecedent_id. The first id is the one with antecedent_id empty

Dataframe example:

id	antecedent_id
id1	id2
id4	id7
id6	id3
id7
id3	id4
id2	id6
id5	id1

The dataframe reordered should be like this:

id	antecedent_id
id7
id4	id7
id3	id4
id6	id3
id2	id6
id1	id2
id5	id1

I would like to find the fastest code to do that as I have a huge number of rows

Thanks you so much for your help !

Welcome to StackOverflow! For future reference, please provide code used to construct the dataframe so that it is easier for people to reproduce your problem statement and answer your question — tnwei
– tnwei, Commented Feb 15, 2022 at 2:38

tnwei · Accepted Answer · 2022-02-15 02:40:58Z

0

You basically want to sort the dataframe by values in a column:

import pandas as pd
df = pd.DataFrame({
    "id": ["id1", "id4", "id6", "id7", "id3", "id2", "id5"],
    "antecedent_id": ["id2", "id7", "id3", "", "id4", "id6", "id1"]
})
sorted_df = df.sort_values("antecedent_id", ascending=False)
print(sorted_df)

This code chunk returns a sorted dataframe like so:

    id antecedent_id
1  id4           id7
5  id2           id6
4  id3           id4
2  id6           id3
0  id1           id2
6  id5           id1
3  id7

answered Feb 15, 2022 at 2:40

tnwei

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1 Comment

kcsquared Over a year ago

I came to the same conclusion initially due to the phrase reorder the dataframe in the right order using antecedent_id, but this is very likely not what OP wanted. The outputs here don't match their expected output. What OP should have said is 'I have a directed graph (actually a path), where each node except the root has a unique antecedent (i.e. ancestor). Find this root, and perform a topological sort of the dataframe rows'

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