breeze.util.Iterators.scala Maven / Gradle / Ivy
package breeze.util
/*
Copyright 2009 David Hall, Daniel Ramage
Licensed under the Apache License, Version 2.0 (the "License")
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
/**
* Utilities and implicits for iterators. Nothing major.
*
* @author dlwh, dramage
*/
object Iterators {
def fromProducer[E](prod: =>Option[E]):Iterator[E] = Iterator.continually(prod).takeWhile(None !=).map(_.get)
/**
* Merges (ordered) iterators by returning the lesser element at the
* head of each, according to the given comparator. Ties go to the element
* from the first iterator.
*/
def merge[T](iters : Iterator[T]*)(compare : ((T,T) => Int)) : Iterator[T] =
new Iterator[T] {
/** Keep track of the top of each list. */
val heads = iters.map(get _).toArray
/** The merged iterator has more if any head is not None. */
override def hasNext : Boolean =
heads.map(_ != None).foldLeft(false)(_||_)
/** Return the smallest element that is currently a list head. */
override def next : T = {
val top = heads.zipWithIndex.foldLeft((None.asInstanceOf[Option[T]],-1)) {
(headA : (Option[T],Int), headB : (Option[T],Int)) =>
(headA, headB) match {
case ((Some(a),i), (Some(b),j)) => if (compare(a,b) <= 0) headA else headB
case ((Some(a),i), (None,j)) => headA
case ((None,i), (Some(b),j)) => headB
case ((None,i), (None,j)) => headA
case x:Any => throw new IllegalStateException(x.toString)
}
}
// update the top list and return its value
heads(top._2) = get(iters(top._2))
return top._1.get
}
def get(iter : Iterator[T]) : Option[T] =
if (iter.hasNext) Some(iter.next) else None
}
}