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August 29, 2015 13:57
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Lazily generate all subsequences of an Iterator or Iterable, up to the specified length, returning a new Iterator.
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import scala.collection.mutable.ListBuffer | |
// See also http://stackoverflow.com/questions/22633598/creating-an-iterator-of-subsequences-from-an-iterator-of-items/ | |
/** Lazily generate all subsequences of an Iterator or Iterable, up to the specified length, returning a new Iterator. */ | |
class Subseqs[A](n: Int)(i: Iterator[A]) extends Iterator[List[A]] { | |
val buffer = new ListBuffer[A]() | |
//buffer ++= i.take(n) // NO - inconsistent behaviour of take() with iterators | |
// see http://stackoverflow.com/questions/7619642/consume-items-from-a-scala-iterator | |
(1 to n).foreach(_ => buffer += i.next()) | |
var index = 1 | |
def hasNext = buffer.length > 1 | |
def next = { | |
def increment() = { val i = index; index += 1; i } | |
if (index > buffer.length) { | |
index = 1 | |
buffer.remove(0) | |
if (i.hasNext) buffer += i.next() | |
} | |
buffer.slice(0, increment()).toList | |
} | |
} | |
/** Pimp my library*/ | |
object Subseqs { | |
implicit class SubseqIterable[A](i: Iterable[A]) { | |
def subseqs(n: Int) = new Subseqs(n)(i.iterator) | |
} | |
implicit class SubseqIterator[A](i: Iterator[A]) { | |
def subseqs(n: Int) = new Subseqs(n)(i) | |
} | |
} |
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