Replies per Help-Desk Ticket

PandasEasyJunior level~10 min

Problem

You are given a DataFrame `messages` with columns `msg_id` and `root_id`. There is no single unique key; the same `msg_id` may appear more than once.

A message with `root_id` equal to NULL (missing) is a brand-new **ticket**. A message with a non-null `root_id` is a **reply**, and `root_id` is the `msg_id` of the ticket it replies to.

For each ticket, report how many **distinct** replies it has. A reply counts once even if its `msg_id` appears multiple times. A reply whose `root_id` does not match any ticket is ignored.

Return `ticket_id` and `reply_count`, ordered by `ticket_id` ascending.

Input data

Example rows — the live problem includes the full dataset.

messages

msg_id	root_id
1
2
1
12
3	1

Expected output

Your answer should return 3 rows with the columns ticket_id, reply_count.

Starter code (Pandas (Python))

import pandas as pd

def replies_per_ticket(messages) -> pd.DataFrame:
    # Your code here
    return messages

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