Created
April 19, 2013 00:27
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Adding Relational Algebra style joins to Scala Traversables.
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import scala.collection.generic.CanBuildFrom | |
import scala.collection.TraversableLike | |
import scala.collection.SeqLike | |
import scala.collection.Seq | |
import Option.empty | |
object TraversableExtensions { | |
implicit class TraversableWithJoin[A, Repr <: Traversable[A]](val xs: TraversableLike[A, Repr]) extends AnyVal { | |
def ⋈[B, J](fA: A => J)(t: Traversable[B])(fB: B => J) { | |
innerJoin(fA)(t)(fB) | |
} | |
def innerJoin[That, B, J](fA: A => J)(t: Traversable[B])(fB: B => J)(implicit bf: CanBuildFrom[Repr, (A, B), That]): That = { | |
val builder = bf(xs.asInstanceOf[Repr]) | |
val left = xs.groupBy(fA); | |
val right = t.groupBy(fB); | |
val keys = left.keySet intersect right.keySet | |
for (key <- keys) { | |
left(key).foreach(l => right(key).foreach(r => builder += Tuple2(l, r))) | |
} | |
builder.result | |
} | |
def ⟕[B, J](fA: A => J)(t: Traversable[B])(fB: B => J) { | |
leftJoin(fA)(t)(fB) | |
} | |
def leftJoin[That, B, J](fA: A => J)(t: Traversable[B])(fB: B => J)(implicit bf: CanBuildFrom[Repr, (A, Option[B]), That]): That = { | |
val builder = bf(xs.asInstanceOf[Repr]) | |
val left = xs.groupBy(fA); | |
val right = t.groupBy(fB); | |
for (leftGroup <- left) { | |
val key = leftGroup._1 | |
val leftElements = leftGroup._2 | |
if (right.contains(key)) { | |
leftElements.foreach(l => right(key).foreach(r => builder += Tuple2(l, Option(r)))) | |
} else { | |
leftElements.foreach(l => builder += Tuple2(l, empty)) | |
} | |
} | |
builder.result | |
} | |
def ⟖[B, J](fA: A => J)(t: Traversable[B])(fB: B => J) { | |
rightJoin(fA)(t)(fB) | |
} | |
def rightJoin[That, B, J](fA: A => J)(t: Traversable[B])(fB: B => J)(implicit bf: CanBuildFrom[Repr, (Option[A], B), That]): That = { | |
val builder = bf(xs.asInstanceOf[Repr]) | |
val left = xs.groupBy(fA); | |
val right = t.groupBy(fB); | |
for (rightGroup <- right) { | |
val key = rightGroup._1 | |
val rightElements = rightGroup._2 | |
if (left.contains(key)) { | |
rightElements.foreach(r => left(key).foreach(l => builder += Tuple2(Option(l), r))) | |
} else { | |
rightElements.foreach(r => builder += Tuple2(empty, r)) | |
} | |
} | |
builder.result | |
} | |
def ⟗[B, J](fA: A => J)(t: Traversable[B])(fB: B => J) { | |
outerJoin(fA)(t)(fB) | |
} | |
def outerJoin[That, B, J](fA: A => J)(t: Traversable[B])(fB: B => J)(implicit bf: CanBuildFrom[Repr, (Option[A], Option[B]), That]): That = { | |
val builder = bf(xs.asInstanceOf[Repr]) | |
val left = xs.groupBy(fA); | |
val right = t.groupBy(fB); | |
val keys = left.keySet ++ right.keySet | |
for (key <- keys) { | |
if (left.contains(key) && right.contains(key)) { | |
left(key).foreach(l => right(key).foreach(r => builder += Tuple2(Option(l), Option(r)))) | |
} else if (left.contains(key)) { | |
left(key).foreach(l => builder += Tuple2(Option(l), empty)) | |
} else { | |
right(key).foreach(r => builder += Tuple2(empty, Option(r))) | |
} | |
} | |
builder.result | |
} | |
} | |
} |
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