Saya hanya mencantumkan fungsi yang setara dari Enumerable<A>
. Ini belum lengkap sampai sekarang. Saya akan mencoba memperbaruinya nanti dengan lebih banyak lagi.
xs.Aggregate(accumFunc) -> xs.reduceLeft(accumFunc)
xs.Aggregate(seed, accumFunc) -> xs.foldLeft(seed)(accumFunc)
xs.Aggregate(seed, accumFunc, trans) -> trans(xs.foldLeft(seed)(accumFunc))
xs.All(pred) -> xs.forall(pred)
xs.Any() -> xs.nonEmpty
xs.Any(pred) -> xs.exists(pred)
xs.AsEnumerable() -> xs.asTraversable // roughly
xs.Average() -> xs.sum / xs.length
xs.Average(trans) -> trans(xs.sum / xs.length)
xs.Cast<A>() -> xs.map(_.asInstanceOf[A])
xs.Concat(ys) -> xs ++ ys
xs.Contains(x) -> xs.contains(x) //////
xs.Contains(x, eq) -> xs.exists(eq(x, _))
xs.Count() -> xs.size
xs.Count(pred) -> xs.count(pred)
xs.DefaultIfEmpty() -> if(xs.isEmpty) List(0) else xs // Use `mzero` (from Scalaz) instead of 0 for more genericity
xs.DefaultIfEmpty(v) -> if(xs.isEmpty) List(v) else xs
xs.Distinct() -> xs.distinct
xs.ElementAt(i) -> xs(i)
xs.ElementAtOrDefault(i) -> xs.lift(i).orZero // `orZero` is from Scalaz
xs.Except(ys) -> xs.diff(ys)
xs.First() -> xs.head
xs.First(pred) -> xs.find(pred) // returns an `Option`
xs.FirstOrDefault() -> xs.headOption.orZero
xs.FirstOrDefault(pred) -> xs.find(pred).orZero
xs.GroupBy(f) -> xs.groupBy(f)
xs.GroupBy(f, g) -> xs.groupBy(f).mapValues(_.map(g))
xs.Intersect(ys) -> xs.intersect(ys)
xs.Last() -> xs.last
xs.Last(pred) -> xs.reverseIterator.find(pred) // returns an `Option`
xs.LastOrDefault() -> xs.lastOption.orZero
xs.LastOrDefault(pred) -> xs.reverseIterator.find(pred).orZero
xs.Max() -> xs.max
xs.Max(f) -> xs.maxBy(f)
xs.Min() -> xs.min
xs.Min(f) -> xs.minBy(f)
xs.OfType<A>() -> xs.collect { case x: A => x }
xs.OrderBy(f) -> xs.sortBy(f)
xs.OrderBy(f, comp) -> xs.sortBy(f)(comp) // `comp` is an `Ordering`.
xs.OrderByDescending(f) -> xs.sortBy(f)(implicitly[Ordering[A]].reverse)
xs.OrderByDescending(f, comp) -> xs.sortBy(f)(comp.reverse)
Enumerable.Range(start, count) -> start until start + count
Enumerable.Repeat(x, times) -> Iterator.continually(x).take(times)
xs.Reverse() -> xs.reverse
xs.Select(trans) -> xs.map(trans) // For indexed overload, first `zipWithIndex` and then `map`.
xs.SelectMany(trans) -> xs.flatMap(trans)
xs.SequenceEqual(ys) -> xs.sameElements(ys)
xs.Skip(n) -> xs.drop(n)
xs.SkipWhile(pred) -> xs.dropWhile(pred)
xs.Sum() -> xs.sum
xs.Sum(f) -> xs.map(f).sum // or `xs.foldMap(f)`. Requires Scalaz.
xs.Take(n) -> xs.take(n)
xs.TakeWhile(pred) -> xs.takeWhile(pred)
xs.OrderBy(f).ThenBy(g) -> xs.sortBy(x => (f(x), g(x))) // Or: xs.sortBy(f &&& g). `&&&` is from Scalaz.
xs.ToArray() -> xs.toArray // Use `xs.toIndexedSeq` for immutable indexed sequence.
xs.ToDictionary(f) -> xs.map(f.first).toMap // `first` is from Scalaz. When f = identity, you can just write `xs.toMap`.
xs.ToList() -> xs.toList // This returns an immutable list. Use `xs.toBuffer` if you want a mutable list.
xs.Union(ys) -> xs.union(ys)
xs.Where(pred) -> xs.filter(pred)
xs.Zip(ys, f) -> (xs, ys).zipped.map(f) // When f = identity, use `xs.zip(ys)`
Tidak ada persamaan langsung untuk beberapa fungsi, tetapi cukup mudah untuk menjalankannya sendiri. Berikut beberapa fungsinya.
Lajang:
def single[A](xs: Traversable[A]): A = {
if(xs.isEmpty) sys error "Empty sequence!"
else if(xs.size > 1) sys error "More than one elements!"
else xs.head
}
SingleOrDefault:
def singleOrDefault[A : Zero](xs: Traversable[A]): A = {
if(xs.isEmpty) mzero
else if(xs.size > 1) sys error "More than one elements!"
else xs.head
}
Bergabung:
def join[A, B, K, R](outer: Traversable[A], inner: Traversable[B])
(outKey: A => K, inKey: B => K, f: (A, B) => R): Traversable[R] = {
for(o <- outer; i <- inner; if outKey(o) == inKey(i)) yield f(o, i)
}
Gabung Grup:
def groupJoin[A, B, K, R](outer: Traversable[A], inner: Traversable[B])
(outKey: A => K, inKey: B => K, f: (A, Traversable[B]) => R): Traversable[R] = {
for(o <- outer) yield {
val zs = for(i <- inner; if outKey(o) == inKey(i)) yield i
f(o, zs)
}
}
Catatan:
Dalam Scala idiomatik, fungsi total umumnya lebih disukai daripada fungsi parsial. Jadi, implementasi idiomatis dari single
dan singleOrDefault
akan menghasilkan nilai bertipe Either[Exception, A]
, bukan A
. Misalnya, berikut adalah implementasi halus dari single
yang mengembalikan Either[Exception, A]
.
def single[A](xs: Traversable[A]): Either[Exception, A] = {
if(xs.isEmpty) Left(new RuntimeException("Empty sequence!"))
else if(xs.size > 1) Left(new RuntimeException("More than one elements!"))
else Right(xs.head)
}
Zero
/mzero
Scalaz tidak sama dengan mekanisme nilai default
C#. Untuk detailnya, Anda dapat merujuk ke ini postingan yang saya tulis tentang topik ini beberapa waktu lalu.
Anda dapat menggunakan pola memperkaya perpustakaan saya untuk mencapai efek yang sama seperti metode ekstensi C#. Lihat ini dan ini untuk detailnya.
person
Community
schedule
12.11.2011