SINQ - Swift Integrated Query

Swift has generic Collections and Sequences as well as some universal free functions to work with them. What is missing is a fluent interface that would make working with them easy¹ - like list comprehensions in many languages or LINQ in .NET. The operations should: require no typecasts, be easily chained, work on any sequences, be performed lazily where possible.

Overview

SINQ (or LINQ for Swift) is a Swift library for working with sequences / collections. It is, as name suggests, modelled after LINQ, but it is not necessarily intended to be a LINQ port. The library is still under development, just as Swift is. Any contributions, both in terms of suggestions/ideas or actual code are welcome.

SINQ is brought to you by Leszek Ślażyński (slazyk), you can follow me on twitter and github. Be sure to check out Observable-Swift my other library that implements value observing and events.

Examples

The main goal of SINQ is to provide a fluent interface for working with collections. The way it tries to accomplish that is with chaining of methods. Most of the operations are performed lazily, i.e. computations are deferred and done only for the part of the result you enumerate. Everything is typed - no typecasts required. Examples:

let nums1 = from([1, 4, 2, 3, 5]).whereTrue{ $0 > 2 }.orderBy{ $0 }.select{ 2 * $0 }
// or less (linq | sql)-esque 
let nums2 = sinq([1, 4, 2, 3, 5]).filter{ $0 > 2 }.orderBy{ $0 }.map{ 2 * $0 }

// path1 : String = ..., path2: String = ...
let commonComponents = sinq(path1.pathComponents)
    .zip(path2.pathComponents) { ($0, $1) }
    .takeWhile { $0 == $1 }
    .count()

let prefixLength = sinq(path1).zip(path2){ ($0, $1) }.takeWhile{ $0 == $1 }.count()

// available : String[] = ..., blacklist : String[] = ...
let next = sinq(available).except(blacklist){ $0 }.firstOrDefault("unknown")

// employees : Employee[] = ...

let headCnt = sinq(employees).groupBy{ $0.manager }.map{ ($0.key, $0.values.count()) }

let allTasks = from(employees).selectMany{ $0.tasks }.orderBy{ $0.priority }

let elite1 = sinq(employees).whereTrue{ $0.salary > 1337 }.orderBy{ $0.salary }
let elite2 = from(employees).orderBy{ $0.salary }.takeWhile{ $0.salary > 1337 }

// products : Product[] = ..., categories : Category[] = ...

let breadcrumbs = sinq(categories).join(inner: products,
                                     outerKey: { $0.id },
                                     innerKey: { $0.categoryId },
                                       result: { "\($0.name) / \($1.name)" })

Please note that the results are not cached, i.e. looping twice over result of orderBy(...) will perform two sorts. If you want to use results multiple times, you can get always array with toArray().

It uses SinqSequence<T> wrapper struct in order to do that, you can wrap any Sequence by simply sinq(seq), from(seq), or SinqSequence(seq). This wrapper is introduced because Swift does not allow for adding methods to protocols (like Sequence) and because extending existing SequenceOf<T> causes linker errors.

While I do try to follow cocoa-like naming and spelling conventions, while also keeping the LINQ naming where reasonable, I refuse to call the struct SINQSequence<T> or SSequence<T>.

Installation

You can use either CocoaPods or Carthage to install SINQ.

Otherwise, the easiest option to use SINQ in your project is to clone this repo and add SINQ.xcodeproj to your project/workspace and then add SINQ.framework to frameworks for your target.

After that you just import SINQ.

List of methods

aggregate / reduce - combine all the elements of the sequence into a result

aggregate(combine: (T, T) -> T) -> T
aggregate<R>(initial: R, combine: (R, T) -> R) -> R
aggregate<C, R>(initial: C, combine: (C, T) -> C, result: C -> R) -> R

all - check if a predicate is true for all the elements

all(predicate: T -> Bool) -> Bool

any - check if not empty, or if a predicate is true for any object

any() -> Bool      
any(predicate: T -> Bool) -> Bool

concat - create a sequence concatenating two sequences

concat<S: Sequence>(other: S) -> SinqSequence<T>

contains - check if the sequence contains an element

contains(value: T, equality: (T, T) -> Bool) -> Bool
contains<K: Equatable>(value: T, key: T -> K) -> Bool

count - count the elements in the sequence

func count() -> Int

distinct - create a sequence with unique elements, in order

distinct(equality: (T, T) -> Bool) -> SinqSequence<T>
distinct<K: Hashable>(key: T -> K) -> SinqSequence<T>

each - iterate over the sequence

each(function: T -> ()) -> ()  

elementAt - get element at given index from the sequence

elementAtOrNil(index: Int) -> T?  
elementAt(index: Int) -> T
elementAt(index: Int, orDefault: T) -> T

except - create sequence with unique elements, excluding given

except<S: Sequence>(sequence: S, equality: (T, T) -> Bool) -> SinqSequence<T> 
except<S: Sequence, K: Hashable>(sequence: S, key: T -> K) -> SinqSequence<T>  

first - get first element of the sequence [satisfying a predicate]

first() -> T
firstOrNil() -> T?
first(predicate: T -> Bool) -> T
firstOrDefault(defaultElement: T) -> T
firstOrNil(predicate: T -> Bool) -> T?
firstOrDefault(defaultElement: T, predicate: T -> Bool) -> T

groupBy - create a sequence grouping elements by given key

groupBy<K: Hashable>(key: T -> K) -> SinqSequence<Grouping<K, T>>
groupBy<K: Hashable, V>(key: T -> K, element: T -> V) -> SinqSequence<Grouping<K, V>>
groupBy<K: Hashable, V, R>(key: T -> K, element: T -> V, result: (K, SinqSequence<V>) -> R) -> SinqSequence<R>

groupJoin - create a sequence joining two sequences with grouping

groupJoin<S: Sequence, K: Hashable>
	(#inner: S, outerKey: T -> K, innerKey: S.E -> K)
	-> SinqSequence<Grouping<T, S.E>>
groupJoin<S: Sequence, K: Hashable, R>
	(#inner: S, outerKey: T -> K, innerKey: S.E -> K,
 	 result: (T, SinqSequence<S.E>) -> R) -> SinqSequence<R>

intersect - create a sequence with unique elements present in both sequences

intersect<S: Sequence>(sequence: S, equality: (T, T) -> Bool) -> SinqSequence<T>
intersect<S: Sequence, K: Hashable>(sequence: S, key: T -> K) -> SinqSequence<T>

join - create a sequence joining two sequences without grouping

join<S: Sequence, K: Hashable, R>
	(#inner: S, outerKey: T -> K, innerKey: S.E -> K,
     result: (T, S.E) -> R) -> SinqSequence<R>
join<S: Sequence, K: Hashable>
    (#inner: S, outerKey: T -> K, innerKey: S.E -> K)
    -> SinqSequence<(T, S.E)>

last - return last element in the sequence [satisfying a predicate]

last() -> T
lastOrNil() -> T?
last(predicate: T -> Bool) -> T
lastOrNil(predicate: T -> Bool) -> T?
lastOrDefault(defaultElement: T) -> T
lastOrDefault(defaultElement: T, predicate: T -> Bool) -> T

min / max - return the minimum/maximum value of a function for the sequence

min<R: Comparable>(key: T -> R) -> R
max<R: Comparable>(key: T -> R) -> R

argmin / argmax - return the element for which the function has the minimum/maximum value

argmin<R: Comparable>(key: T -> R) -> T
argmax<R: Comparable>(key: T -> R) -> T

orderBy / orderByDescending - create a sequence sorted by given key

orderBy<K: Comparable>(key: T -> K) -> SinqOrderedSequence<T>
orderByDescending<K: Comparable>(key: T -> K) -> SinqOrderedSequence<T>

reverse - create a sequence with reverse order

reverse() -> SinqSequence<T>

select / map - create a sequence with results of applying given function

select<V>(selector: T -> V) -> SinqSequence<V>
select<V>(selector: (T, Int) -> V) -> SinqSequence<V>

selectMany - create a sequence by concatenating function results for each element

selectMany<S: Sequence>(selector: T -> S) -> SinqSequence<S.E>
selectMany<S: Sequence>(selector: (T, Int) -> S) -> SinqSequence<S.E>
selectMany<S: Sequence, R>(selector: T -> S, result: S.E -> R) -> SinqSequence<R>
selectMany<S: Sequence, R>(selector: (T, Int) -> S, result: S.E -> R) -> SinqSequence<R>

single - return the only element in a sequence containing exactly one element

single() -> T
singleOrNil() -> T?
singleOrDefault(defaultElement: T) -> T
single(predicate: T -> Bool) -> T
singleOrNil(predicate: T -> Bool) -> T?
singleOrDefault(defaultElement: T, predicate: T -> Bool) -> T

skip - create a sequence skipping (given number of elements | while predicate holds )

skip(count: Int) -> SinqSequence<T>
skipWhile(predicate: T -> Bool) -> SinqSequence<T>

take - create a sequence by taking (given number of elements | while predicate holds )

take(count: Int) -> SinqSequence<T>
takeWhile(predicate: T -> Bool) -> SinqSequence<T>

thenBy / thenByDescending - create a sequence by additionally sorting on given key

thenBy<K: Comparable>(key: T -> K) -> SinqOrderedSequence<T>
thenByDescending<K: Comparable>(key: T -> K) -> SinqOrderedSequence<T>

toArray - create an array from the sequence

toArray() -> T[]

toDictionary / toLookupDictionary - create a dictionary from the sequence

toDictionary<K: Hashable, V>(keyValue: T -> (K, V)) -> Dictionary<K, V>
toDictionary<K: Hashable, V>(key: T -> K, value: T -> V) -> Dictionary<K, V>
toDictionary<K: Hashable>(key: T -> K) -> Dictionary<K, T>

union - create a sequence with unique elements from either of the sequences

union<S: Sequence>(sequence: S, equality: (T, T) -> Bool) -> SinqSequence<T>
union<S: Sequence, K: Hashable>(sequence: S, key: T -> K) -> SinqSequence<T>

whereTrue / filter - create a sequence only with elements satisfying a predicate

whereTrue(predicate: T -> Bool) -> SinqSequence<T>

zip - create a sequence by combining pairs of elements from two sequences

zip<S: Sequence, R>(sequence: S, result: (T, S.E) -> R) -> SinqSequence<R>

Troubleshooting

Due to bug in swift it sometimes happens that swift compiler and/or SourceKitService loop indefinitely while solving type constraints during compilation or indexing. If this happens, to help them solve the constraints, one might have to divide work for them into smaller pieces. For example this would cause inifinite loop:

func testAll() {
  XCTAssertTrue(sinq([11, 12, 15, 10]).all{ $0 >= 10 })
  XCTAssertFalse(sinq([11, 12, 15, 10]).all{ $0 > 10 })
}

While this does not:

func testAll() {
  let seq = sinq([11, 12, 15, 10])
  XCTAssertTrue(seq.all{ $0 >= 10 })
  XCTAssertFalse(seq.all{ $0 < 13 })
}

In this case it seems o be connected to @auto_closure arguments of XCTAssert*...

In case it happens for you, try to divide the statements like this or be more explicit in code about types and not depend as much on type inference.

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¹ - this statement might become less true in the future, e.g. in Beta 4 Apple introduced lazy() which is similar to subset of sinq() in that it adds lazy chainable .map .filter .reverse .array and subscripting.