Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
R-Style Boolean Sequence Selectors in Swift
extension Sequence where Element: Comparable {
static func ==(_ lhs: Self, _ rhs: Element) -> LazyMapSequence<Self, Bool> {
lhs.lazy.map { $0 == rhs }
}
static func !=(_ lhs: Self, _ rhs: Element) -> LazyMapSequence<Self, Bool> {
lhs.lazy.map { $0 != rhs }
}
static func <(_ lhs: Self, _ rhs: Element) -> LazyMapSequence<Self, Bool> {
lhs.lazy.map { $0 < rhs }
}
static func <=(_ lhs: Self, _ rhs: Element) -> LazyMapSequence<Self, Bool> {
lhs.lazy.map { $0 <= rhs }
}
static func >(_ lhs: Self, _ rhs: Element) -> LazyMapSequence<Self, Bool> {
lhs.lazy.map { $0 > rhs }
}
static func >=(_ lhs: Self, _ rhs: Element) -> LazyMapSequence<Self, Bool> {
lhs.lazy.map { $0 >= rhs }
}
}
struct Broadcasted<Base: Collection>: Collection where Base.Index: BinaryInteger {
typealias Element = Base.Element
typealias Index = Base.Index
private var base: Base
private var count_: Index
var startIndex: Index { 0 }
var endIndex: Index { count_ }
func index(after i: Index) -> Index { i + 1 }
subscript(index: Index) -> Element {
base[index % Index(base.count)]
}
init(_ base: Base, count: Index) {
self.base = base
self.count_ = count
}
}
extension Collection {
subscript<C>(selection: C) -> [Element] where C: Collection, C.Index: BinaryInteger, C.Element == Bool {
zip(Broadcasted(selection, count: C.Index(count)), self)
.filter(\.0).map(\.1)
}
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment