Dart - 21 - Collection Functions (map, filter, reduce)

Collection Functions in Dart: map, filter, and reduce

Collection functions are powerful tools in Dart that allow you to transform, filter, and aggregate data within iterable collections such as lists, sets, and maps. In this discussion, we’ll explore three key collection functions: map, filter, and reduce. These functions play a crucial role in processing data efficiently and elegantly in Dart applications.

The map Function

The map function in Dart is used to create a new collection by applying a function to each element in an existing iterable. It transforms each element of the collection into a new value, and the results are collected into a new iterable. This is useful when you need to modify or derive values from an iterable.

Here’s an example of using the map function to double the values of a list of numbers:


var numbers = [1, 2, 3, 4, 5];
var doubledNumbers = numbers.map((number) => number * 2).toList();

print(doubledNumbers); // Outputs: [2, 4, 6, 8, 10]

The filter Function

The filter function is used to create a new collection by selecting elements from an existing iterable that satisfy a given condition. It retains elements that meet the specified criteria and discards those that don’t. This is valuable for extracting specific elements from a collection.

Here’s an example of using the filter function to extract even numbers from a list of integers:


var numbers = [1, 2, 3, 4, 5, 6];
var evenNumbers = numbers.where((number) => number % 2 == 0).toList();

print(evenNumbers); // Outputs: [2, 4, 6]

The reduce Function

The reduce function is employed to aggregate the elements of an iterable into a single value. It repeatedly applies a function to pairs of elements, accumulating the results until a final value is obtained. This is especially useful for calculating sums, products, or other aggregations.

Here’s an example of using the reduce function to find the sum of elements in a list of numbers:


var numbers = [1, 2, 3, 4, 5];
var sum = numbers.reduce((value, element) => value + element);

print(sum); // Outputs: 15

Chaining Collection Functions

Dart allows you to chain multiple collection functions together, creating a sequence of operations to transform, filter, and aggregate data. This enables elegant and efficient data processing in a single line of code.

Here’s an example of chaining map and filter functions to transform and filter a list of words:


var words = ['apple', 'banana', 'cherry', 'date', 'elderberry'];
var result = words
    .map((word) => word.toUpperCase())
    .where((word) => word.startsWith('A'))
    .toList();

print(result); // Outputs: ['APPLE']

Handling Edge Cases

When working with collection functions, it’s essential to consider edge cases, such as empty collections or operations that may result in errors. Dart provides mechanisms to handle these scenarios, such as providing initial values for reduce and using isEmpty to check for empty collections before applying functions.

Here’s an example of using an initial value with the reduce function:


var numbers = [];
var sum = numbers.fold(0, (value, element) => value + element);

print(sum); // Outputs: 0 (initial value)

Conclusion

Collection functions like map, filter, and reduce are essential tools for manipulating data within iterable collections in Dart. These functions enable you to transform, filter, and aggregate data efficiently and elegantly, simplifying complex data processing tasks. Whether you’re modifying elements, extracting specific values, or calculating aggregations, mastering these functions is valuable for developing Dart applications.

Dart – 21 – Collection Functions (map, filter, reduce)