Inventory Snapshot

Part of the Logic & Flow section of Coddy's Ruby journey — lesson 55 of 56.

An inventory report that exercises hashes, Enumerable chains, group_by, and a touch of formatting.

Challenge

Medium

The array inventory is given. Each item is a hash with :name, :category, :qty, and :price.

Print four lines:

Total inventory value across all items (qty * price, summed), printed as an integer.
The category with the highest item count, in the format Top category: <name> (<count>). Ties broken alphabetically by category name.
Names of items out of stock (qty == 0), sorted alphabetically, joined with , . If none, print (none).
Names of the top 3 most expensive items by unit price, highest first, joined with , . Ties broken by name alphabetically.

For the default inventory the output is:

232
Top category: food (3)
milk
chair, lamp, milk

Cheat sheet

Working with arrays of hashes using Enumerable methods:

# Sum with calculation per element
inventory.sum { |item| item[:qty] * item[:price] }

# Group by a key and count
groups = inventory.group_by { |item| item[:category] }
groups.max_by { |cat, items| [items.count, ...] }

# Filter, sort, and join
inventory.select { |item| item[:qty] == 0 }
         .map { |item| item[:name] }
         .sort
         .join(", ")

# Sort by multiple criteria (ties broken alphabetically)
inventory.sort_by { |item| [-item[:price], item[:name]] }
         .first(3)
         .map { |item| item[:name] }
         .join(", ")

Breaking ties alphabetically when using max_by with counts:

# Higher count wins; on tie, alphabetically first (negate string for max_by)
groups.max_by { |cat, items| [items.count, -cat.ord] }
# Or use min_by on negated count + natural string order
groups.sort_by { |cat, items| [-items.count, cat] }.first

Try it yourself

inventory = [
  { name: "apple",  category: "food",        qty: 10, price: 2 },
  { name: "bread",  category: "food",        qty: 4,  price: 3 },
  { name: "milk",   category: "food",        qty: 0,  price: 4 },
  { name: "chair",  category: "furniture",   qty: 2,  price: 35 },
  { name: "lamp",   category: "furniture",   qty: 5,  price: 20 },
  { name: "pencil", category: "stationery",  qty: 30, price: 1 }
]

# TODO: print total value, top category, out-of-stock names, top 3 by price