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Filtering is a powerful feature in functional programming that allows you to refine and manipulate datasets efficiently, ensuring that only elements meeting specific criteria are retained for further processing.
Throughout this series, you will encounter various scenarios that challenge you to apply List.filter. Each exercise is crafted to help you deepen your grasp of list transformations and to gain familiarity with Elm's strong type system and functional programming paradigm.
- Understand the Basics: Learn how to use
List.filterto apply simple conditions to data. - Handle Complex Data Structures: Practice filtering data that includes custom types and nested structures.
- Develop Problem-Solving Skills: Each exercise provides a unique problem scenario encouraging you to think critically about how to apply filtering effectively.
- Enhance Code Clarity and Safety: Emphasize writing clear and maintainable code using Elm’s type system.
- Each exercise will provide a dataset and a task focusing on a specific filtering challenge.
- Think critically about the conditions under which data should be included in your result.
- Try to use Elm’s custom types where applicable to improve type safety and code readability.
By the end of this series, you should feel confident in your ability to manipulate and filter data effectively using Elm, preparing you for more advanced programming tasks and real-world applications.
Task: Write a function to filter out all even numbers from a list of integers.
- Input:
[1, 2, 3, 4, 5, 6, 7, 8]
Output:[1, 3, 5, 7] - Input:
[12, 14, 15, 19, 20, 21]
Output:[15, 19, 21] - Input:
[2, 4, 6, 8, 10]
Output:[] - Input:
[11, 22, 33, 44, 55]
Output:[11, 33, 55]
Task: Create a function to exclude words shorter than 4 characters from a list of strings.
- Input:
["apple", "is", "good", "for", "you"]
Output:["apple", "good"] - Input:
["elm", "is", "fun", "to", "learn"]
Output:["learn"] - Input:
["chat", "at", "openai", "with", "gpt"]
Output:["chat", "openai", "with"] - Input:
["this", "is", "a", "list", "of", "words"]
Output:["this", "list", "words"]
Task: Develop a function to filter out scores below 75 from a list of student scores.
- Input:
[70, 82, 89, 90, 55, 78]
Output:[82, 89, 90, 78] - Input:
[60, 73, 69, 85, 91]
Output:[85, 91] - Input:
[74, 75, 76, 50, 49, 90]
Output:[75, 76, 90] - Input:
[100, 95, 85, 65, 60, 55]
Output:[100, 95, 85]
Task: Create a function to filter out words that start with the letter 'A', regardless of case, from a list of strings.
- Input:
["Apple", "banana", "Avocado", "grape", "apricot"]
Output:["banana", "grape"] - Input:
["almond", "Peach", "apricot", "orange", "acorn"]
Output:["Peach", "orange"] - Input:
["Banana", "apple", "avocado"]
Output:["Banana"] - Input:
["apron", "antelope", "bison", "ant"]
Output:["bison"]
Task: Filter out all words that do NOT start with the letter 'A', regardless of case, from a list of strings.
- Input:
["Apple", "banana", "Avocado", "grape", "apricot"]
Output:["Apple", "Avocado", "apricot"] - Input:
["almond", "Peach", "apricot", "orange", "acorn"]
Output:["almond", "apricot", "acorn"] - Input:
["Banana", "apple", "avocado"]
Output:["apple", "avocado"] - Input:
["apron", "antelope", "bison", "ant"]
Output:["apron", "antelope", "ant"]
Task: Write a function that filters out all people under 18 years old or whose gender is not specified as female from a list of person records. Each person record should include a name, age, and a gender.
- Input:
[{name = "Alice", age = 25, gender = Female}, {name = "Bob", age = 17, gender = Male}, {name = "Carol", age = 15, gender = Female}]
Output:[{name = "Alice", age = 25, gender = Female}] - Input:
[{name = "Dave", age = 30, gender = Male}, {name = "Eve", age = 20, gender = Female}]
Output:[{name = "Eve", age = 20, gender = Female}] - Input:
[{name = "Fred", age = 16, gender = Male}, {name = "George", age = 21, gender = Male}, {name = "Helen", age = 19, gender = Female}]
Output:[{name = "Helen", age = 19, gender = Female}] - Input:
[{name = "Hannah", age = 14, gender = Female}, {name = "Ian", age = 13, gender = Male}, {name = "Jill", age = 19, gender = Male}]
Output:[]
Task: Remove all non-positive numbers (zero and negatives) from a list of integers.
- Input:
[-10, 0, 5, 20, -30, 0, 40]
Output:[5, 20, 40] - Input:
[1, 2, 3, -1, -2, 0]
Output:[1, 2, 3] - Input:
[-50, -60, -70]
Output:[] - Input:
[0, 0, 0, 0, 100]
Output:[100]
Task: Filter out all numbers that are not multiples of five from a list of integers.
- Input:
[10, 22, 30, 47, 55, 60]
Output:[10, 30, 55, 60] - Input:
[5, 11, 15, 23, 25, 40]
Output:[5, 15, 25, 40] - Input:
[1, 2, 3, 4, 5, 10, 15]
Output:[5, 10, 15] - Input:
[12, 14, 19, 21, 22]
Output:[]
Task: Write a function to exclude all elements whose length is not 5 from a list of lists.
- Input:
[[1, 2, 3, 4, 5], [6, 7, 8], [9, 10, 11, 12, 13], [14, 15]]
Output:[[1, 2, 3, 4, 5], [9, 10, 11, 12, 13]] - Input:
[[1, 2, 3], [4, 5, 6, 7, 8], [9, 10], [11, 12, 13, 14, 15]]
Output:[[4, 5, 6, 7, 8], [11, 12, 13, 14, 15]] - Input:
[[1], [2], [3, 4, 5, 6, 7], [8, 9, 10, 11, 12]]
Output:[[3, 4, 5, 6, 7], [8, 9, 10, 11, 12]] - Input:
[[1, 2, 3, 4], [5, 6, 7, 8, 9], [10], [11, 12, 13, 14, 15, 16]]
Output:[[5, 6, 7, 8, 9]]
Task: From a list of tasks, filter out all tasks that are not marked as pending.
Tasks can be marked as completed, pending, in progress, or under review.
- Input:
[{task = "Email client", status = Completed}, {task = "Update website", status = Pending}, {task = "Call supplier", status = InProgress}, {task = "Prepare report", status = Pending}]
Output:[{task = "Update website", status = Pending}, {task = "Prepare report", status = Pending}] - Input:
[{task = "Fix bugs", status = Pending}, {task = "Deploy app", status = Completed}, {task = "Review code", status = Pending}]
Output:[{task = "Fix bugs", status = Pending}, {task = "Review code", status = Pending}] - Input:
[{task = "Plan sprint", status = Completed}, {task = "Write tests", status = InProgress}]
Output:[] - Input:
[{task = "Schedule meeting", status = Pending}, {task = "Update docs", status = Completed}, {task = "Design logo", status = Review}]
Output:[{task = "Schedule meeting", status = Pending}]
Task: Filter out all strings that do not exist in the form <first-part>@<second-part>.<third-part> from a list of potential email addresses.
- Input:
["alice@example.com", "bob@example", "carol@site.com", "dave@web"]
Output:["alice@example.com", "carol@site.com"] - Input:
["user@domain.com", "admin@", "@example.com", "info@test.com"]
Output:["user@domain.com", "info@test.com"] - Input:
["name@company.com", "employee@", "boss@office.com"]
Output:["name@company.com", "boss@office.com"] - Input:
["@", "support@example.com", "contact@site"]
Output:["support@example.com"]
Task: Filter out all users from a list who do not have 'admin' level permissions. Assume each user record includes fields for full name, username, and permission level.
- Input:
[{fullName = "Alice Smith", username = "alice", permission = Admin}, {fullName = "Bob Johnson", username = "bob", permission = User}, {fullName = "Carol White", username = "carol", permission = Admin}]
Output:[{fullName = "Alice Smith", username = "alice", permission = Admin}, {fullName = "Carol White", username = "carol", permission = Admin}] - Input:
[{fullName = "Dave Brown", username = "dave", permission = User}, {fullName = "Eve Black", username = "eve", permission = Admin}, {fullName = "Frank Ray", username = "frank", permission = Guest}]
Output:[{fullName = "Eve Black", username = "eve", permission = Admin}] - Input:
[{fullName = "Grace Lee", username = "grace", permission = User}, {fullName = "Helen Green", username = "helen", permission = User}]
Output:[] - Input:
[{fullName = "Ian Grey", username = "ian", permission = Admin}, {fullName = "Jill Gold", username = "jill", permission = Admin}, {fullName = "Kelly Fox", username = "kelly", permission = User}]
Output:[{fullName = "Ian Grey", username = "ian", permission = Admin}, {fullName = "Jill Gold", username = "jill", permission = Admin}]
Task: Remove all products from a list that are priced above $5.00. Assume each product record includes fields for product name, category, and price.
- Input:
[{productName = "Milk", category = "Dairy", price = 4.99}, {productName = "Cheese", category = "Dairy", price = 6.50}, {productName = "Butter", category = "Dairy", price = 5.49}]
Output:[{productName = "Milk", category = "Dairy", price = 4.99}] - Input:
[{productName = "Bread", category = "Bakery", price = 3.49}, {productName = "Cake", category = "Bakery", price = 7.99}]
Output:[{productName = "Bread", category = "Bakery", price = 3.49}] - Input:
[{productName = "Yogurt", category = "Dairy", price = 0.99}, {productName = "Ice cream", category = "Frozen", price = 5.99}]
Output:[{productName = "Yogurt", category = "Dairy", price = 0.99}] - Input:
[{productName = "Pasta", category = "Grocery", price = 2.50}, {productName = "Olive oil", category = "Grocery", price = 10.99}]
Output:[{productName = "Pasta", category = "Grocery", price = 2.50}]
Task: Remove all products from a list whose price, when converted to U.S. dollars, is above $5.00. Each product record includes a price that is a record with fields for amount and currency. Use the provided conversion rates to convert prices to U.S. dollars before filtering.
- EUR to USD: 1.18
- GBP to USD: 1.31
- CAD to USD: 0.79
- Input:
[{productName = "Milk", category = "Dairy", price = {amount = 4.00, currency = USD}}, {productName = "Cheese", category = "Dairy", price = {amount = 5.00, currency = EUR}}]
Output:[{productName = "Milk", category = "Dairy", price = {amount = 4.00, currency = USD}}] - Input:
[{productName = "Bread", category = "Bakery", price = {amount = 3.00, currency = USD}}, {productName = "Butter", category = "Dairy", price = {amount = 6.00, currency = GBP}}]
Output:[{productName = "Bread", category = "Bakery", price = {amount = 3.00, currency = USD}}] - Input:
[{productName = "Yogurt", category = "Dairy", price = {amount = 6.50, currency = CAD}}, {productName = "Ice cream", category = "Frozen", price = {amount = 5.50, currency = CAD}}]
Output:[] - Input:
[{productName = "Pasta", category = "Grocery", price = {amount = 4.50, currency = USD}}, {productName = "Olive oil", category = "Grocery", price = {amount = 7.00, currency = EUR}}]
Output:[{productName = "Pasta", category = "Grocery", price = {amount = 4.50, currency = USD}}]
Task: Filter out all animals that do not live in aquatic habitat from a list. Assume each animal record includes fields for name, species, and habitat.
Context: The possible habitats for animals are as follows:
- Aquatic: For animals living primarily in water, like sharks and whales.
- Terrestrial: For land-dwelling animals, such as bears and rabbits.
- Arboreal: For animals that live in trees, like tree frogs.
- Input:
[{name = "Shark", species = "Great White Shark", habitat = Aquatic}, {name = "Eagle", species = "Bald Eagle", habitat = Terrestrial}]
Output:[{name = "Shark", species = "Great White Shark", habitat = Aquatic}] - Input:
[{name = "Dolphin", species = "Bottlenose Dolphin", habitat = Aquatic}, {name = "Bear", species = "Grizzly Bear", habitat = Terrestrial}]
Output:[{name = "Dolphin", species = "Bottlenose Dolphin", habitat = Aquatic}] - Input:
[{name = "Whale", species = "Blue Whale", habitat = Aquatic}, {name = "Frog", species = "Tree Frog", habitat = Arboreal}]
Output:[{name = "Whale", species = "Blue Whale", habitat = Aquatic}] - Input:
[{name = "Otter", species = "Sea Otter", habitat = Aquatic}, {name = "Rabbit", species = "Cottontail Rabbit", habitat = Terrestrial}]
Output:[{name = "Otter", species = "Sea Otter", habitat = Aquatic}]
Task: Exclude all items from a list that do not have a specific tag attached. Assume each item record includes fields for item name, price, and a list of tags. Your function should be able to filter by just any tag that's passed to it as argument.
For example, if we're filtering by the tag 'Portable':
- Input:
[{itemName = "Laptop", price = 1200, tags = [Electronics, Portable]}, {itemName = "Desk", price = 450, tags = [Furniture]}]
Output:[{itemName = "Laptop", price = 1200, tags = [Electronics, Portable]}] - Input:
[{itemName = "Smartphone", price = 999, tags = [Electronics, Mobile, Portable]}, {itemName = "Chair", price = 150, tags = [Furniture]}]
Output:[{itemName = "Smartphone", price = 999, tags = [Electronics, Mobile, Portable]}] - Input:
[{itemName = "Backpack", price = 70, tags = [Portable, Travel]}, {itemName = "Sofa", price = 1200, tags = [Furniture, Comfort]}]
Output:[{itemName = "Backpack", price = 70, tags = [Portable, Travel]}] - Input:
[{itemName = "Tablet", price = 600, tags = [Electronics, Portable]}, {itemName = "Bookcase", price = 320, tags = [Furniture]}]
Output:[{itemName = "Tablet", price = 600, tags = [Electronics, Portable]}]
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