Python Data Analysis Code Review

I have completed a Python data-analysis assignment that relies on Pandas, NumPy, and Matplotlib, and I want a fresh set of expert eyes on it before submission. The brief is already met functionally, but I need a critical review that:

• checks code structure, logic flow, and edge-case handling
• flags any inefficient operations (especially within Pandas transformations and NumPy calculations)
• confirms that visualisations generated with Matplotlib follow best practices for clarity and reproducibility
• includes concise, inline comments or a short report explaining suggested improvements and why they matter

Please keep the original file hierarchy intact and return either a pull-request style diff or commented scripts so I can see every change in context. Accuracy, readability, and performance are the priorities.