Top 10 Array utility methods you should know (Dart) 🎯

As part of my venture in client-side application development with Dart, I began exploring how one could go about working with Array/List types. Aside from the documentation being comprehensive, I was also able to find support on the StackOverflow community and successfully achieved what was needed.

In today’s article we’ll be looking at the “batteries-included” notion of Dart, in particular, the inbuilt utilities for working with Lists. I’ve hand-picked 10 of the most common ones you show know for your next app. I’ve also prepared the example snippets so you could play with those yourself 😁

So, shall we begin?

1. forEach()

Runs a function on each element in the list

var fruits = ['banana', 'pineapple', 'watermelon'];
fruits.forEach((fruit) => print(fruit)); // => banana pineapple watermelon

2. map()

Produces a new list after transforming each element in a given list

var mappedFruits = fruits.map((fruit) => 'I love $fruit').toList();
print(mappedFruits); // => ['I love banana', 'I love pineapple', 'I love watermelon']

3. contains()

Checks to confirm that the given element is in the list

var numbers = [1, 3, 2, 5, 4];
print(numbers.contains(2)); // => true

4. sort()

Orders the elements in a list based on the provided ordering function

numbers.sort((num1, num2) => num1 - num2); // => [1, 2, 3, 4, 5]

5. reduce(), fold()

Compresses the elements of a list to a single value, using a given function

var sum = numbers.reduce((current, next) => current + next);
print(sum); // => 15

// with fold() you provide an initial value
const initialValue = 10;
var sum2 = numbers.fold(initialValue, (current, next) => current + next);
print(sum2); // => 25

6. every()

Confirms that every element satisfies the test

List<Map<String, dynamic>> users = [
  { "name": 'John', "age": 18 },
  { "name": 'Jane', "age": 21 },
  { "name": 'Mary', "age": 23 },
];

var is18AndOver = users.every((user) => user["age"] >= 18);
print(is18AndOver); // => true

var hasNamesWithJ = users.every((user) => user["name"].startsWith('J'));
print(hasNamesWithJ); // => false

7. where(), firstWhere(), singleWhere()

Returns a collection of elements that satisfy a test

// See #6 for users list
var over21s = users.where((user) => user["age"] > 21);
print(over21s.length); // => 1

var nameJ = users.firstWhere((user) => user["name"].startsWith('J'), orElse: () => null);
print(nameJ); // => {name: John, age: 18}

var under18s = users.singleWhere((user) => user["age"] < 18, orElse: () => null);
print(under18s); // => null

firstWhere() returns the first match in the list, while singleWhere() returns the first match provided there is exactly one match.

8. take(), skip()

Returns a collection while including or skipping elements

var fiboNumbers = [1, 2, 3, 5, 8, 13, 21];
print(fiboNumbers.take(3).toList()); // => [1, 2, 3]
print(fiboNumbers.skip(5).toList()); // => [13, 21]
print(fiboNumbers.take(3).skip(2).take(1).toList()); // => [3]

9. List.from()

Creates a new list from the given collection

var clonedFiboNumbers = List.from(fiboNumbers);
print('Cloned list: $clonedFiboNumbers');

As of Dart 2.0, the new keyword is optional when instantiating objects.

10. expand()

Expands each element into zero or more elements

var pairs = [[1, 2], [3, 4]];
var flattened = pairs.expand((pair) => pair).toList();
print('Flattened result: $flattened'); // => [1, 2, 3, 4]

var input = [1, 2, 3];
var duplicated = input.expand((i) => [i, i]).toList();
print(duplicated); // => [1, 1, 2, 2, 3, 3]

Conclusion

I hope this has been insightful and if this is your first exposure to Dart, read my first steps tutorial to grasp the basics. The example snippets for this article are available on DartPad.

Like and follow me😍 for more content on Dart.

And this concludes the tutorial. Thanks for reading.

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