Get Neighbors implementation for Undirected and Directed Graphs with Tests

snap-core/graph.cpp

@@ -203,6 +203,43 @@ bool TUNGraph::IsOk(const bool& ThrowExcept) const {
   return RetVal;
 }
 
+void TUNGraph::GetNeighbors(const int& NId, TIntV& NeighborsIdV){
+  //check if the node exists
+  AssertR(IsNode(NId), TStr::Fmt("NodeId %d does not exist", NId));
+
+  //get the snap node corresponding to nodeId
+  TNode& Node = GetNode(NId);
+
+  int neighborCount = Node.GetDeg();
+
+  NeighborsIdV.Gen(neighborCount, 0);
+
+  //go through the entire degree (as it is undirected) of this node
+  //NEdges -= Node.GetDeg();
+
+  for (int e = 0; e < Node.GetDeg(); e++) {
+
+    const int nbr = Node.GetNbrNId(e);
+
+    if (nbr == NId) 
+    { 
+        continue; 
+    }
+
+    TNode& N = GetNode(nbr);
+
+    const int n = N.NIdV.SearchBin(NId);
+
+    IAssert(n != -1); // if NId points to N, then N also should point back
+
+    //add neighbor to neighbors list
+    if (n != -1) { 
+      NeighborsIdV.Add(nbr); 
+    }
+
+  } 
+}
+
 // Print the graph in a human readable form to an output stream OutF.
 void TUNGraph::Dump(FILE *OutF) const {
   const int NodePlaces = (int) ceil(log10((double) GetNodes()));
@@ -434,6 +471,57 @@ bool TNGraph::IsOk(const bool& ThrowExcept) const {
   return RetVal;
 }
 
+void TNGraph::GetNeighbors(const int& NId, TIntV& NeighborsIdV, bool outDegreeNeighbors){
+  //check if the node exists
+  AssertR(IsNode(NId), TStr::Fmt("NodeId %d does not exist", NId));
+
+  //get the snap node corresponding to nodeId
+  TNode& Node = GetNode(NId);
+
+  int neighborCount = 0;
+
+  if(outDegreeNeighbors){
+      neighborCount = Node.GetOutDeg();
+  }
+  else{
+      neighborCount = Node.GetInDeg();
+  }
+
+  NeighborsIdV.Gen(neighborCount, 0);
+
+  //go through the entire degree (as it is undirected) of this node
+  for (int e = 0; e < neighborCount; e++) {
+    int nbr; 
+
+    if(outDegreeNeighbors){
+      nbr = Node.GetOutNId(e);
+    }
+    else{
+      nbr = Node.GetInNId(e);
+    }
+
+    if (nbr == NId) 
+    { 
+        continue; 
+    }
+
+    TNode& N = GetNode(nbr);
+
+    if(outDegreeNeighbors){
+        const int n = N.InNIdV.SearchBin(NId);
+        if (n != -1) { 
+          NeighborsIdV.Add(nbr);
+        }
+    }
+    else{
+        const int n = N.OutNIdV.SearchBin(NId);
+        if (n != -1) { 
+          NeighborsIdV.Add(nbr);
+        }
+    }
+  }
+}
+
 void TNGraph::Dump(FILE *OutF) const {
   const int NodePlaces = (int) ceil(log10((double) GetNodes()));
   fprintf(OutF, "-------------------------------------------------\nDirected Node Graph: nodes: %d, edges: %d\n", GetNodes(), GetEdges());

snap-core/graph.h

@@ -239,6 +239,8 @@ class TUNGraph {
   void Defrag(const bool& OnlyNodeLinks=false);
   /// Checks the graph data structure for internal consistency. ##TUNGraph::IsOk
   bool IsOk(const bool& ThrowExcept=true) const;
+  /// Fills in the neighbor list of the node in the provided vector ##TUNGraph::GetNeighbors
+  void GetNeighbors(const int& NId, TIntV& NeighborsIdV);
   /// Print the graph in a human readable form to an output stream OutF.
   void Dump(FILE *OutF=stdout) const;
   /// Returns a small graph on 5 nodes and 5 edges. ##TUNGraph::GetSmallGraph
@@ -325,6 +327,7 @@ class TNGraph {
     bool IsOutNId(const int& NId) const { return NodeHI.GetDat().IsOutNId(NId); }
     /// Tests whether node with ID NId is a neighbor of the current node.
     bool IsNbrNId(const int& NId) const { return IsOutNId(NId) || IsInNId(NId); }
+
     friend class TNGraph;
   };
   /// Edge iterator. Only forward iteration (operator++) is supported.
@@ -470,6 +473,8 @@ class TNGraph {
   void Defrag(const bool& OnlyNodeLinks=false);
   /// Checks the graph data structure for internal consistency. ##TNGraph::IsOk
   bool IsOk(const bool& ThrowExcept=true) const;
+  /// Fills in the neighbor list of the node in the provided vector ##TNGraph::GetNeighbors
+  void GetNeighbors(const int& NId, TIntV& NeighborsIdV, bool outDegreeNeighbors=true);
   /// Print the graph in a human readable form to an output stream OutF.
   void Dump(FILE *OutF=stdout) const;
   /// Returns a small graph on 5 nodes and 6 edges. ##TNGraph::GetSmallGraph

test/test-TNGraph.cpp

@@ -157,5 +157,39 @@ TEST(TNGraph, GetSmallGraph) {
 
   EXPECT_EQ(1,Graph->IsOk());
   EXPECT_EQ(0,Graph->Empty());
+  EXPECT_EQ(1,Graph->HasFlag(gfDirected));
+}
+
+// Test Neighbors
+TEST(TNGraph, TestNeighbors) {
+  PNGraph Graph;
+
+  Graph = TNGraph::GetSmallGraph();
+
+  TIntV NeighborNodeIds;
+
+  Graph->GetNeighbors(0, NeighborNodeIds);
+
+  TNGraph::TNodeI NodeI = Graph->GetNI(0);
+  int degree = NodeI.GetOutDeg();
+  std::set<int> st; 
+
+  for(int i=0;i<degree;i++){
+    std::cout<<"The "<<i<<"th neighbor of Node 1 is "<<NeighborNodeIds[i]<<std::endl; 
+    st.insert(NeighborNodeIds[i]);
+  }
+
+  //only 2 neightbors should be present (0 & 2)
+  EXPECT_EQ(1, st.find(1) != st.end());
+  st.erase(1);
+
+  EXPECT_EQ(1, st.find(2) != st.end());
+  st.erase(2);
+
+  //check if null now
+  EXPECT_EQ(1, st.empty());
+
+  EXPECT_EQ(1,Graph->IsOk());
+
   EXPECT_EQ(1,Graph->HasFlag(gfDirected));
 }

test/test-TUNGraph.cpp

@@ -1,6 +1,7 @@
 #include <gtest/gtest.h>
 
 #include "Snap.h"
+#include<set>
 
 // Test the default constructor
 TEST(TUNGraph, DefaultConstructor) {
@@ -288,5 +289,39 @@ TEST(TUNGraph, GetSmallGraph) {
 
   EXPECT_EQ(1,Graph->IsOk());
   EXPECT_EQ(0,Graph->Empty());
+  EXPECT_EQ(0,Graph->HasFlag(gfDirected));
+}
+
+// Test Neighbors
+TEST(TUNGraph, TestNeighbors) {
+  PUNGraph Graph;
+
+  Graph = TUNGraph::GetSmallGraph();
+
+  TIntV NeighborNodeIds;
+
+  Graph->GetNeighbors(1, NeighborNodeIds);
+
+  TUNGraph::TNodeI NodeI = Graph->GetNI(1);
+  int degree = NodeI.GetDeg();
+  std::set<int> st; 
+
+  for(int i=0;i<degree;i++){
+    std::cout<<"The "<<i<<"th neighbor of Node 1 is "<<NeighborNodeIds[i]<<std::endl; 
+    st.insert(NeighborNodeIds[i]);
+  }
+
+  //only 2 neightbors should be present (0 & 2)
+  EXPECT_EQ(1, st.find(0) != st.end());
+  st.erase(0);
+
+  EXPECT_EQ(1, st.find(2) != st.end());
+  st.erase(2);
+
+  //check if null now
+  EXPECT_EQ(1, st.empty());
+
+  EXPECT_EQ(1,Graph->IsOk());
+
   EXPECT_EQ(0,Graph->HasFlag(gfDirected));
 }