ADDED reversed arrays for directed graphs to find in-neighbors in con…

…stant time (#79)
Bears-R-Us · Dec 13, 2023 · bb42931 · bb42931
1 parent 3ea51a0
commit bb42931
Show file tree

Hide file tree

Showing 3 changed files with 51 additions and 2 deletions.
diff --git a/arachne/client/arachne/graphclasses.py b/arachne/client/arachne/graphclasses.py
@@ -532,7 +532,7 @@ def add_edges_from(self, akarray_src:pdarray, akarray_dst:pdarray,
         dst = all_vertices[src.size:]
 
         ### Create vertex index arrays.
-        # 1. Build the neighbors of the adjacency lists for each vertex.
+        # 1. Build the out-neighbors of the adjacency lists for each vertex.
         gb_src = ak.GroupBy(src, assume_sorted = True)
         gb_src_indices, gb_src_neighbors = gb_src.count()
         neis = ak.full(gb_vertices.unique_keys.size, 0, dtype=ak.int64)
@@ -547,11 +547,31 @@ def add_edges_from(self, akarray_src:pdarray, akarray_dst:pdarray,
         self.n_vertices = int(vmap.size)
         self.n_edges = int(src.size)
 
+        ### Create the reversed arrays for in-neighbor calculations.
+        # 1. Reverse the edges and sort them.
+        gb_edges_reversed = ak.GroupBy([dst, src])
+        src_reversed = gb_edges_reversed.unique_keys[0]
+        dst_reversed = gb_edges_reversed.unique_keys[1]
+
+        # 2. Build the in-neighbors of the adjacency lists for each vertex.
+        gb_src_reversed = ak.GroupBy(src_reversed, assume_sorted = True)
+        gb_src_indices_reversed, gb_src_neighbors_reversed = gb_src_reversed.count()
+        neis_reversed = ak.full(gb_vertices.unique_keys.size, 0, dtype=ak.int64)
+        neis_reversed[gb_src_indices_reversed] = gb_src_neighbors_reversed
+
+        # 3. Run a prefix (cumulative) sum on neis to get the starting indices for each vertex.
+        segs_reversed = ak.cumsum(neis_reversed)
+        first_seg_reversed = ak.array([0])
+        segs_reversed = ak.concatenate([first_seg_reversed, segs_reversed])
+
         ### Store everything in a graph object in the Chapel server.
         # 1. Store data into an Graph object in the Chapel server.
         args = { "AkArraySrc" : src,
                  "AkArrayDst" : dst,
                  "AkArraySeg" : segs,
+                 "AkArraySrcR" : src_reversed,
+                 "AkArrayDstR" : dst_reversed,
+                 "AkArraySegR" : segs_reversed,
                  "AkArrayWeight" : wgt,
                  "AkArrayVmap" : vmap,
                  "Directed": bool(self.directed),

diff --git a/arachne/server/BuildGraphMsg.chpl b/arachne/server/BuildGraphMsg.chpl
@@ -47,8 +47,8 @@ module BuildGraphMsg {
         // Parse the message from the Python front-end.
         var akarray_srcS = msgArgs.getValueOf("AkArraySrc");
         var akarray_dstS = msgArgs.getValueOf("AkArrayDst");
-        var akarray_vmapS = msgArgs.getValueOf("AkArrayVmap");
         var akarray_segS = msgArgs.getValueOf("AkArraySeg");
+        var akarray_vmapS = msgArgs.getValueOf("AkArrayVmap");
         var akarray_weightS = msgArgs.getValueOf("AkArrayWeight");
         var weightedS = msgArgs.getValueOf("Weighted");
         var directedS = msgArgs.getValueOf("Directed");
@@ -136,6 +136,30 @@ module BuildGraphMsg {
             }
         }
 
+        var akarray_srcRS, akarray_dstRS, akarray_segRS:string;
+        if directed {
+            akarray_srcRS = msgArgs.getValueOf("AkArraySrcR");
+            akarray_dstRS = msgArgs.getValueOf("AkArrayDstR");
+            akarray_segRS = msgArgs.getValueOf("AkArraySegR");
+
+            var akarray_srcR_entry: borrowed GenSymEntry = getGenericTypedArrayEntry(akarray_srcRS, st);
+            var akarray_dstR_entry: borrowed GenSymEntry = getGenericTypedArrayEntry(akarray_dstRS, st);
+            var akarray_segR_entry: borrowed GenSymEntry = getGenericTypedArrayEntry(akarray_segRS, st);
+
+            var akarray_srcR_sym = toSymEntry(akarray_srcR_entry,int);
+            var srcR = akarray_srcR_sym.a;
+
+            var akarray_dstR_sym = toSymEntry(akarray_dstR_entry,int);
+            var dstR = akarray_dstR_sym.a;
+
+            var akarray_segR_sym = toSymEntry(akarray_segR_entry, int);
+            var segmentsR = akarray_segR_sym.a;
+
+            graph.withComp(new shared SymEntry(srcR):GenSymEntry, "SRC_R")
+                .withComp(new shared SymEntry(dstR):GenSymEntry, "DST_R")
+                .withComp(new shared SymEntry(segmentsR):GenSymEntry, "SEGMENTS_R");
+        }
+
         // Create the ranges array that keeps track of the vertices the edge arrays store on each
         // locale.
         var D_sbdmn = {0..numLocales-1} dmapped Replicated();

diff --git a/arachne/server/GraphArray.chpl b/arachne/server/GraphArray.chpl
@@ -34,6 +34,11 @@ module GraphArray {
         EDGE_PROPS_DTYPE_MAP,   // Sorted array of column datatype to integer id (array index)
         EDGE_PROPS_COL2DTYPE,   // Map of column names to the datatype of the column
 
+        // For directed graphs we also want to maintain reversed edge arrays to easily find the
+        // in-neighbors for each vertex. We will use the SRC_R and DST_R components below to 
+        // signify the reversed edge arrays as well as a SEGMENTS_R array defined here. 
+        SEGMENTS_R,
+
         // TEMPORARY COMPONENTS BELOW FOR UNDIRECTED GRAPHS TO ENSURE COMPATIBILTIY WITH OLD CODE.
         // We want to phase out the need for reversed arrays in undirected graph algorithms.
         // Includes: connected components, triangle counting, k-truss, and triangle centrality.