darq 0.4.0

The power of lazy-evaluated enumerables in your hands! (A port of functional LINQ from the .NET library.)

A port of .NET's LINQ IEnumerable functions to Dart. This library extends the native Iterable type with all of the LINQ methods that do not exist in native Dart.

API Reference

• Dart Docs

Usage

Because this library uses Dart 2.6's new extension methods, any Iterable has access to these methods as though they were native methods. This includes classes that extend from Iterable, such as List and Set.

In addition, this library adds several new types of Iterable classes to make some utility functions easier:

// Creates an iterable containing the numbers from 2 to 6: [2, 3, 4, 5, 6]
var rangeI = RangeIterable(2, 6, inclusive: true);

// Creates an iterable that contains 3 copies of the value 'abc': ['abc', 'abc', 'abc']
var repeatI = RepeatIterable('abc', 3);

// Creates an iterable from a string, iterating over its characters
// This is an extension getter property on String that returns an 
// iterable via `String.codeUnits.map((u) => String.fromCodeUnit(u))`.
// Results in ['a', 'b', 'c', 'd', 'e', 'f']
var stringI = 'abcdef'.iterable;

// Same as above but using `runes` instead of `codeUnits` to respect 
// rune boundaries and maintain surrogate pairs.
var stringIR = 'abcdef'.iterableRunes;

You can call any of 40 new methods on it to modify or analyze it. For example, the native method map is expanded upon with select, which combines the element with the index at which the element is found within the iterable:

var list = [10, 20, 30];
var mappedList = list.select((i, index) => '$index-$i'); // ['1-10', '2-20', '3-30']

There are "OrDefault" variants on several common iterator value getter methods, such as firstOrDefault, singleOrDefault, and defaultIfEmpty. Instead of throwing an error, these methods will return a default value (or null if left unspecified) if the element(s) cannot be found:

var list = <String>[];

var native = list.first; // Throws a StateError
var orDefault = list.firstOrDefault('abc'); // Returns 'abc'

var list2 = [1, 2, 3];
var importantValue = list2.where((i) => i >= 4)
                          .defaultIfEmpty(-1); // Returns [-1]

You can filter an iterable down to unique instances of elements with the distinct method:

var list = [1, 1, 1, 2, 2, 3, 4, 5, 5, 5, 5, 5];
var uniqueList = myEnum.distinct(); // [1, 2, 3, 4, 5]

There are also set operations with the except, intersect, and union methods:

var listA = [1, 2, 3, 4];
var listB = [3, 4, 5, 6];

var exclusion = listA.except(listB);       // [1, 2]
var intersection = listA.intersect(listB); // [3, 4]
var union = listA.union(listB);            // [1, 2, 3, 4, 5, 6]

And you can group elements together by common features using groupBy:

var list = [1, 2, 3, 4, 5, 6];
var groupedList = list.groupBy((i) => i / 3 == 0); // [[1, 2, 4, 5], [3, 6]]

Or bundle them into groups of a fixed length using segment:

var list = [1, 2, 3, 4, 5, 6];
var segmented = list.segment(2); // [[1, 2], [3, 4], [5, 6]]

You can even perform complex ordering functions using orderBy and thenBy:

var list = ['ab', 'a', 'c', 'aa', ''];
// Sort by string length followed by alphabetical order
var ordered = list.orderBy((c) => c.length)
                  .thenBy((c) => c);
// Result: ['', 'a', 'c', 'aa', 'ab']

Just like in native dart, every method returns a new Iterable, so you can chain methods together to make complex mapping, grouping, and filtering behavior:

var list = [3, 1, 6, 2, 3, 2, 4, 1];
var result = list.select((i, idx) => i * 2 + idx)     // [6, 3, 14, 8, 10, 10, 14, 9]
                 .distinct()                          // [6, 3, 14, 8, 10, 9]
                 .where((i) => i > 4)                 // [6, 14, 8, 10, 9]
                 .orderBy((i) => i)                   // [6, 8, 9, 10, 14]
                 .map((i) => i.toRadixString(16));    // [6, 8, 9, A, E]

Full Function List

• aggregate
• all
• append
• average
• concat
• count
• defaultIfEmpty
• distinct
• elementAtOrDefault
• except
• firstWhereOrDefault
• firstOrDefault
• groupBy
• groupByValue
• groupJoin
• groupSelect
• groupSelectValue
• intersect
• joinMap
• lastOrDefault
• lastWhereOrDefault
• max
• min
• ofType
• orderBy
• orderByDescending
• prepend
• reverse
• segment
• select
• selectMany
• sequenceEqual
• singleOrDefault
• singleWhereOrDefault
• sum
• thenBy
• thenByDescending
• toMap
• union
• zip