exercism/elixir/boutique-inventory

Boutique Inventory

Welcome to Boutique Inventory on Exercism's Elixir Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Introduction

Enum

Enum is a very useful module that provides a set of algorithms for working with enumerables. It offers sorting, filtering, grouping, counting, searching, finding min/max values, and much more.

In general, an enumerable is any data that can be iterated over, a collection. In Elixir, an enumerable is any data type that implements the Enumerable protocol. The most common of those are lists and maps.

Many Enum functions accept a function as an argument.

Enum.all?([1, 2, 3, 4, 5], fn x -> x > 3 end)
# => false

The most common Enum functions are map and reduce.

map/2

Enum.map/2 allows you to replace every element in an enumerable with another element. The second argument to Enum.map/2 is a function that accepts the original element and returns its replacement.

reduce/3

Enum.reduce/3 allows you to reduce the whole enumerable to a single value. To achieve this, a special variable called the accumulator is used. The accumulator carries the intermediate state of the reduction between iterations.

The second argument to Enum.reduce/3 is the initial value of the accumulator. The third argument is a function that accepts an element and an accumulator, and returns the new value for the accumulator.

Working with maps

When using maps with Enum functions, the map gets automatically converted to a list of 2 {key, value} tuples.

To transform it back to a map, use Enum.into/2. Enum.into/2 is a function that transforms an enumerable into a collectable - any data structure implementing the Collectable protocol. It can be thought of as the opposite of Enum.reduce/3.

Enum also has Enum.into/3. Enum.into/3 is a variation of Enum.into/2 that accepts a transformation function to be applied while transforming the enumerable into a collectable.

Mapping maps

Instead of using Enum.into/3 or Enum.map/2 plus Enum.into/1 to apply a transformation (mapping) to a map, we can also use a dedicated Map.new/2 function. It works exactly like Enum.into/3 in that it accepts an enumerable and a transformation function, but it always returns a new map instead of letting us choose a collectible.

Instructions

You are running an online fashion boutique. Your big annual sale is coming up, so you need to take stock of your inventory to make sure you're ready.

A single item in the inventory is represented by a map, and the whole inventory is a list of such maps.

%{
  name: "White Shirt",
  price: 40,
  quantity_by_size: %{s: 3, m: 7, l: 8, xl: 4}
}

1. Sort items by price

Implement the sort_by_price/1 function. It should take the inventory and return it sorted by item price, ascending.

BoutiqueInventory.sort_by_price([
  %{price: 65, name: "Maxi Brown Dress", quantity_by_size: %{}},
  %{price: 50, name: "Red Short Skirt", quantity_by_size: %{}},
  %{price: 50, name: "Black Short Skirt", quantity_by_size: %{}},
  %{price: 20, name: "Bamboo Socks Cats", quantity_by_size: %{}}
])
# => [
#      %{price: 20, name: "Bamboo Socks Cats", quantity_by_size: %{}},
#      %{price: 50, name: "Red Short Skirt", quantity_by_size: %{}},
#      %{price: 50, name: "Black Short Skirt", quantity_by_size: %{}},
#      %{price: 65, name: "Maxi Brown Dress", price: 65, quantity_by_size: %{}}
#    ]

2. Find all items with missing prices

After sorting your inventory by price, you noticed that you must have made a mistake when you were taking stock and forgot to fill out prices for a few items.

Implement the with_missing_price/1 function. It should take the inventory and return a list of items that do not have prices.

BoutiqueInventory.with_missing_price([
  %{price: 40, name: "Black T-shirt", quantity_by_size: %{}},
  %{price: nil, name: "Denim Pants", quantity_by_size: %{}},
  %{price: nil, name: "Denim Skirt", quantity_by_size: %{}},
  %{price: 40, name: "Orange T-shirt", quantity_by_size: %{}}
])
# => [
#      %{price: nil, name: "Denim Pants", quantity_by_size: %{}},
#      %{price: nil, name: "Denim Skirt", quantity_by_size: %{}}
#    ]

3. Update item names

You noticed that some item names have a word that you don't like to use anymore. Now you need to update all the item names with that word.

Implement the update_names/3 function. It should take the inventory, the old word that you want to remove, and a new word that you want to use instead. It should return a list of items with updated names.

BoutiqueInventory.update_names(
  [
    %{price: 40, name: "Black T-shirt", quantity_by_size: %{}},
    %{price: 70, name: "Denim Pants", quantity_by_size: %{}},
    %{price: 65, name: "Denim Skirt", quantity_by_size: %{}},
    %{price: 40, name: "Orange T-shirt", quantity_by_size: %{}}
  ],
  "T-shirt",
  "Tee"
)
# => [
#      %{price: 40, name: "Black Tee", quantity_by_size: %{}},
#      %{price: 70, name: "Denim Pants", quantity_by_size: %{}},
#      %{price: 65, name: "Denim Skirt", quantity_by_size: %{}},
#      %{price: 40, name: "Orange Tee", quantity_by_size: %{}}
#    ]

4. Increment the item's quantity

Some items were selling especially well, so you ordered more, in all sizes.

Implement the increase_quantity/2 function. It should take a single item and a number n, and return that item with the quantity for each size increased by n.

BoutiqueInventory.increase_quantity(
 %{
   name: "Polka Dot Skirt",
   price: 68,
   quantity_by_size: %{s: 3, m: 5, l: 3, xl: 4}
 },
 6
)
# => %{
#      name: "Polka Dot Skirt",
#      price: 68,
#      quantity_by_size: %{l: 9, m: 11, s: 9, xl: 10}
#    }

5. Calculate the item's total quantity

To know how much space you need in your storage, you need to know how many of each item you have in total.

Implement the total_quantity/1 function. It should take a single item and return how many pieces you have in total, in any size.

BoutiqueInventory.total_quantity(%{
  name: "Red Shirt",
  price: 62,
  quantity_by_size: %{s: 3, m: 6, l: 5, xl: 2}
})
# => 16

Source

Created by

• @angelikatyborska

Contributed to by

• @neenjaw
• @fmmatheus