Cumulative Downloads per Platform

Problem

You are given a DataFrame `dailyinstalls` with columns `app_name`, `platform`, `log_day`, and `installs`. The pair `(platform, log_day)` is unique, and each row gives the number of installs recorded for an app on a given platform (such as 'iOS' or 'Android') on a given day.

For each platform and each day, report the **running total of installs** on that platform up to and including that day. Name the running total `cumulative_installs`.

Return `platform`, `log_day`, and `cumulative_installs`, ordered by `platform`, then by `log_day`.

**Example**

```text
dailyinstalls:
+----------+----------+------------+----------+
| app_name | platform | log_day | installs |
+----------+----------+------------+----------+
| Lumio | iOS | 2022-05-01 | 100 |
| Pixly | Android | 2022-05-01 | 50 |
| Lumio | iOS | 2022-05-02 | 30 |
| Pixly | Android | 2022-05-02 | 40 |
+----------+----------+------------+----------+

Result:
+----------+------------+---------------------+
| platform | log_day | cumulative_installs |
+----------+------------+---------------------+
| Android | 2022-05-01 | 50 |
| Android | 2022-05-02 | 90 |
| iOS | 2022-05-01 | 100 |
| iOS | 2022-05-02 | 130 |
+----------+------------+---------------------+
```

Input data

Example rows — the live problem includes the full dataset.

Expected output

Your answer should return 4 rows with the columns platform, log_day, cumulative_installs.

Starter code (Pandas (Python))

import pandas as pd

def cumulative_downloads_per_platform(dailyinstalls) -> pd.DataFrame:
    # Your code here
    return dailyinstalls

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