175 lines
6.6 KiB
Markdown
175 lines
6.6 KiB
Markdown
# Boutique Inventory
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Welcome to Boutique Inventory on Exercism's Elixir Track.
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If you need help running the tests or submitting your code, check out `HELP.md`.
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If you get stuck on the exercise, check out `HINTS.md`, but try and solve it without using those first :)
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## Introduction
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## Enum
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`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.
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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][exercism-protocols]. The most common of those are [lists][exercism-lists] and [maps][exercism-maps].
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Many `Enum` functions accept a function as an argument.
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```elixir
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Enum.all?([1, 2, 3, 4, 5], fn x -> x > 3 end)
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# => false
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```
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The most common `Enum` functions are `map` and `reduce`.
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### `map/2`
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`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.
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### `reduce/3`
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`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.
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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.
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### Working with maps
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When using maps with `Enum` functions, the map gets automatically converted to a list of 2 `{key, value}` tuples.
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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`.
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`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.
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#### Mapping maps
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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.
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[exercism-protocols]: https://exercism.org/tracks/elixir/concepts/protocols
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[exercism-lists]: https://exercism.org/tracks/elixir/concepts/lists
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[exercism-maps]: https://exercism.org/tracks/elixir/concepts/maps
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## Instructions
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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.
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A single item in the inventory is represented by a map, and the whole inventory is a list of such maps.
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```elixir
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%{
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name: "White Shirt",
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price: 40,
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quantity_by_size: %{s: 3, m: 7, l: 8, xl: 4}
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}
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```
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## 1. Sort items by price
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Implement the `sort_by_price/1` function. It should take the inventory and return it sorted by item price, ascending.
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```elixir
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BoutiqueInventory.sort_by_price([
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%{price: 65, name: "Maxi Brown Dress", quantity_by_size: %{}},
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%{price: 50, name: "Red Short Skirt", quantity_by_size: %{}},
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%{price: 50, name: "Black Short Skirt", quantity_by_size: %{}},
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%{price: 20, name: "Bamboo Socks Cats", quantity_by_size: %{}}
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])
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# => [
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# %{price: 20, name: "Bamboo Socks Cats", quantity_by_size: %{}},
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# %{price: 50, name: "Red Short Skirt", quantity_by_size: %{}},
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# %{price: 50, name: "Black Short Skirt", quantity_by_size: %{}},
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# %{price: 65, name: "Maxi Brown Dress", price: 65, quantity_by_size: %{}}
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# ]
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```
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## 2. Find all items with missing prices
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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.
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Implement the `with_missing_price/1` function. It should take the inventory and return a list of items that do not have prices.
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```elixir
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BoutiqueInventory.with_missing_price([
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%{price: 40, name: "Black T-shirt", quantity_by_size: %{}},
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%{price: nil, name: "Denim Pants", quantity_by_size: %{}},
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%{price: nil, name: "Denim Skirt", quantity_by_size: %{}},
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%{price: 40, name: "Orange T-shirt", quantity_by_size: %{}}
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])
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# => [
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# %{price: nil, name: "Denim Pants", quantity_by_size: %{}},
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# %{price: nil, name: "Denim Skirt", quantity_by_size: %{}}
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# ]
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```
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## 3. Update item names
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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.
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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.
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```elixir
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BoutiqueInventory.update_names(
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[
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%{price: 40, name: "Black T-shirt", quantity_by_size: %{}},
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%{price: 70, name: "Denim Pants", quantity_by_size: %{}},
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%{price: 65, name: "Denim Skirt", quantity_by_size: %{}},
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%{price: 40, name: "Orange T-shirt", quantity_by_size: %{}}
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],
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"T-shirt",
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"Tee"
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)
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# => [
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# %{price: 40, name: "Black Tee", quantity_by_size: %{}},
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# %{price: 70, name: "Denim Pants", quantity_by_size: %{}},
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# %{price: 65, name: "Denim Skirt", quantity_by_size: %{}},
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# %{price: 40, name: "Orange Tee", quantity_by_size: %{}}
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# ]
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```
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## 4. Increment the item's quantity
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Some items were selling especially well, so you ordered more, in all sizes.
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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`.
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```elixir
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BoutiqueInventory.increase_quantity(
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%{
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name: "Polka Dot Skirt",
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price: 68,
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quantity_by_size: %{s: 3, m: 5, l: 3, xl: 4}
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},
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6
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)
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# => %{
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# name: "Polka Dot Skirt",
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# price: 68,
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# quantity_by_size: %{l: 9, m: 11, s: 9, xl: 10}
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# }
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```
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## 5. Calculate the item's total quantity
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To know how much space you need in your storage, you need to know how many of each item you have in total.
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Implement the `total_quantity/1` function. It should take a single item and return how many pieces you have in total, in any size.
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```elixir
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BoutiqueInventory.total_quantity(%{
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name: "Red Shirt",
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price: 62,
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quantity_by_size: %{s: 3, m: 6, l: 5, xl: 2}
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})
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# => 16
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```
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## Source
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### Created by
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- @angelikatyborska
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### Contributed to by
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- @neenjaw
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- @fmmatheus |