Refactor getAllUniqueCombinations avoid nested loops

CHANGELOG.md

@@ -41,6 +41,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Switched from `osm4scala` to `openstreetmap.osmosis` [#409](https://github.com/ie3-institute/OSMoGrid/issues/409)
 - Changed transformer input parameter to PSDM requirements [#417](https://github.com/ie3-institute/OSMoGrid/issues/417)
 - Adapted run initialization [#404](https://github.com/ie3-institute/OSMoGrid/issues/404)
+- Refactoring of 'getAllUniqueCombinations' to avoid nested loops [#431](https://github.com/ie3-institute/OSMoGrid/issues/431)
 
 ### Fixed
 - Fixed bug in `LvGridGeneratorSupport` [#388](https://github.com/ie3-institute/OSMoGrid/issues/388)

src/main/scala/utils/Connections.scala

@@ -6,6 +6,7 @@
 
 package utils
 
+import com.typesafe.scalalogging.LazyLogging
 import edu.ie3.datamodel.graph.{DistanceWeightedEdge, DistanceWeightedGraph}
 import edu.ie3.datamodel.models.input.NodeInput
 import edu.ie3.datamodel.models.input.connector.LineInput
@@ -26,6 +27,7 @@ import utils.OsmoGridUtils.getAllUniqueCombinations
 
 import javax.measure.quantity.Length
 import scala.collection.mutable
+import scala.collection.parallel.CollectionConverters._
 import scala.jdk.CollectionConverters._
 
 /** This utility object contains all known [[Connection]]s.
@@ -101,7 +103,7 @@ case class Connections[T](
   }
 }
 
-object Connections {
+object Connections extends LazyLogging {
   val log: Logger = LoggerFactory.getLogger(Connections.getClass)
 
   /** Utility object for connections.
@@ -201,23 +203,34 @@ object Connections {
     val vertexes = graph.vertexSet().asScala
     val paths = vertexes.map { v => v -> shortestPath.getPaths(v) }.toMap
 
-    getAllUniqueCombinations(graph.vertexSet().asScala.toList).map {
-      case (nodeA, nodeB) =>
-        val path = paths(nodeA).getPath(nodeB)
+    if (vertexes.size > 1000)
+      logger.info(
+        s"Needs to find shortest path connections for ${vertexes.size} vertices. This may take a while."
+      )
+    val connections =
+      getAllUniqueCombinations(graph.vertexSet().asScala.toList).par.map {
+        case (nodeA, nodeB) =>
+          val path = paths(nodeA).getPath(nodeB)
+
+          if (path == null) {
+            throw GridException(
+              s"No path could be found between $nodeA and $nodeB, because either node is not connected to the graph."
+            )
+          }
 
-        if (path == null) {
-          throw GridException(
-            s"No path could be found between $nodeA and $nodeB, because either node is not connected to the graph."
+          Connection(
+            nodeA,
+            nodeB,
+            Quantities.getQuantity(path.getWeight, Units.METRE),
+            Some(path)
           )
-        }
-
-        Connection(
-          nodeA,
-          nodeB,
-          Quantities.getQuantity(path.getWeight, Units.METRE),
-          Some(path)
-        )
-    }
+
+      }.toList
+    if (vertexes.size > 1000)
+      logger.info(
+        s"Finished search for shortest path connections for ${vertexes.size} vertices."
+      )
+    connections
   }
 
   /** Method for creating undirected [[Connection]]s. Excluding connections that

src/main/scala/utils/OsmoGridUtils.scala

@@ -8,12 +8,7 @@ package utils
 
 import edu.ie3.datamodel.models.OperationTime
 import edu.ie3.datamodel.models.input.connector.Transformer2WInput
-import edu.ie3.datamodel.models.input.container.{
-  GraphicElements,
-  JointGridContainer,
-  RawGridElements,
-  SystemParticipants
-}
+import edu.ie3.datamodel.models.input.container.JointGridContainer
 import edu.ie3.datamodel.models.input.{NodeInput, OperatorInput}
 import edu.ie3.datamodel.models.voltagelevels.VoltageLevel
 import edu.ie3.osmogrid.cfg.OsmoGridConfig.Voltage
@@ -34,7 +29,6 @@ import org.locationtech.jts.geom.{Coordinate, Polygon}
 import tech.units.indriya.ComparableQuantity
 import tech.units.indriya.unit.Units
 
-import java.util
 import java.util.UUID
 import javax.measure.quantity.{Area, Power}
 import scala.collection.parallel.ParSeq
@@ -139,36 +133,17 @@ object OsmoGridUtils {
     * @return
     *   a list of all unique connections
     */
-  def getAllUniqueCombinations[T](
-      nodes: List[T]
-  ): List[(T, T)] = {
+  def getAllUniqueCombinations[T](nodes: List[T]): List[(T, T)] = {
     if (nodes.size < 2) {
       List.empty
-    } else if (nodes.size == 2) {
-      List((nodes(0), nodes(1)))
     } else {
-      val connections: util.List[(T, T)] =
-        new util.ArrayList[(T, T)]
-
-      // algorithm to find all unique combinations
-      nodes.foreach(nodeA => {
-        nodes.foreach(nodeB => {
-          // it makes no sense to connect a node to itself => nodeA and nodeB cannot be the same
-          if (nodeA != nodeB) {
-            // two combinations possible
-            val t1 = (nodeA, nodeB)
-            val t2 = (nodeB, nodeA)
-
-            // if none of the combinations is already added, the first combination is added
-            if (!connections.contains(t1) && !connections.contains(t2)) {
-              connections.add(t1)
-            }
-          }
-        })
-      })
-
-      // returns all unique connections
-      connections.asScala.toList
+      for {
+        // Loops through all nodes as a and combines each node a with each b
+        // of the same nodes list. Nodes as b are restricted to those that
+        // occur later in the list than each node a respectively.
+        (a, i) <- nodes.zipWithIndex
+        b <- nodes.drop(i + 1)
+      } yield (a, b)
     }
   }