fix(polygonize): Migrate edge storage from Array to Map for performance

packages/turf-polygonize/lib/Graph.ts

@@ -42,10 +42,9 @@ function validateGeoJson(geoJson: AllGeoJSON) {
  * This graph is directed (both directions are created)
  */
 class Graph {
-  private nodes = new Set<Node>();
-  private nodeIdx: Map<number, Map<number, Node>> = new Map(); // Map<longitude, Map<latitude, Node>>
+  private nodes: Map<number, Map<number, Node>> = new Map(); // Map<longitude, Map<latitude, Node>>
   private nodeId = 0; // the next node id to use
-  private edges: Edge[] = [];
+  private edges = new Map<Node, Map<Node, Edge>>(); // Map<from, Map<to, Edge>>
 
   /**
    * Creates a graph from a GeoJSON.
@@ -88,15 +87,14 @@ class Graph {
    * @returns {Node} - The created or stored node
    */
   getNode(coordinates: number[]) {
-    let node = this.nodeIdx.get(coordinates[0])?.get(coordinates[1]);
+    let node = this.nodes.get(coordinates[0])?.get(coordinates[1]);
 
     if (node == null) {
       const node = new Node(this.nodeId++, coordinates);
-      this.nodes.add(node);
-      let byLat = this.nodeIdx.get(coordinates[0]);
+      let byLat = this.nodes.get(coordinates[0]);
       if (byLat == null) {
         byLat = new Map();
-        this.nodeIdx.set(coordinates[0], byLat);
+        this.nodes.set(coordinates[0], byLat);
       }
       byLat.set(coordinates[1], node);
       return node;
@@ -117,17 +115,28 @@ class Graph {
     const edge = new Edge(from, to),
       symetricEdge = edge.getSymetric();
 
-    this.edges.push(edge);
-    this.edges.push(symetricEdge);
+    // add the forward edge
+    let toMap = this.edges.get(from);
+    if (toMap == null) {
+      toMap = new Map();
+      this.edges.set(from, toMap);
+    }
+    toMap.set(to, edge);
+
+    // add the symmetric edge
+    let symToMap = this.edges.get(to);
+    if (symToMap == null) {
+      symToMap = new Map();
+      this.edges.set(to, symToMap);
+    }
+    symToMap.set(from, symetricEdge);
   }
 
   /**
    * Removes Dangle Nodes (nodes with grade 1).
    */
   deleteDangles() {
-    for (const node of this.nodes) {
-      this._removeIfDangle(node);
-    }
+    this._forEachNode((node) => this._removeIfDangle(node));
   }
 
   /**
@@ -158,7 +167,7 @@ class Graph {
     this._findLabeledEdgeRings();
 
     // Cut-edges (bridges) are edges where both edges have the same label
-    this.edges.forEach((edge) => {
+    this._forEachEdge((edge) => {
       if (edge.label === edge.symetric!.label) {
         this.removeEdge(edge.symetric!);
         this.removeEdge(edge);
@@ -176,9 +185,7 @@ class Graph {
    */
   _computeNextCWEdges(node?: Node) {
     if (node == null) {
-      for (const node of this.nodes) {
-        this._computeNextCWEdges(node);
-      }
+      this._forEachNode((node) => this._computeNextCWEdges(node));
     } else {
       node.getOuterEdges().forEach((edge, i) => {
         node.getOuterEdge(
@@ -242,7 +249,7 @@ class Graph {
   _findLabeledEdgeRings() {
     const edgeRingStarts: Edge[] = [];
     let label = 0;
-    this.edges.forEach((edge) => {
+    this._forEachEdge((edge) => {
       if (edge.label! >= 0) return;
 
       edgeRingStarts.push(edge);
@@ -268,7 +275,7 @@ class Graph {
     this._computeNextCWEdges();
 
     // Clear labels
-    this.edges.forEach((edge) => {
+    this._forEachEdge((edge) => {
       edge.label = undefined;
     });
 
@@ -282,7 +289,7 @@ class Graph {
     const edgeRingList: EdgeRing[] = [];
 
     // find all edgerings
-    this.edges.forEach((edge) => {
+    this._forEachEdge((edge) => {
       if (edge.ring) return;
       edgeRingList.push(this._findEdgeRing(edge));
     });
@@ -342,8 +349,7 @@ class Graph {
   removeNode(node: Node) {
     node.getOuterEdges().forEach((edge) => this.removeEdge(edge));
     node.innerEdges.forEach((edge) => this.removeEdge(edge));
-    this.nodeIdx.get(node.coordinates[0])?.delete(node.coordinates[1]);
-    this.nodes.delete(node);
+    this.nodes.get(node.coordinates[0])?.delete(node.coordinates[1]);
   }
 
   /**
@@ -352,9 +358,25 @@ class Graph {
    * @param {Edge} edge - Edge to be removed
    */
   removeEdge(edge: Edge) {
-    this.edges = this.edges.filter((e) => !e.isEqual(edge));
+    this.edges.get(edge.from)?.delete(edge.to);
     edge.deleteEdge();
   }
+
+  _forEachNode(fn: (n: Node) => void) {
+    for (const latMap of this.nodes.values()) {
+      for (const node of latMap.values()) {
+        fn(node);
+      }
+    }
+  }
+
+  _forEachEdge(fn: (e: Edge) => void) {
+    for (const toMap of this.edges.values()) {
+      for (const edge of toMap.values()) {
+        fn(edge);
+      }
+    }
+  }
 }
 
 export { Graph };