Array Methods Workout

Setup

You are given an array of order objects with id, customer, total and status fields.

Tasks

1. Return only shipped orders.
2. Compute revenue for each customer.
3. Find the highest-value order without mutating the source array.
4. Group orders by status.
5. Produce a flat list of line items across all orders.

Rules

Prefer pure functions. Avoid for loops unless the task explicitly benefits from early exit.