diff --git a/CSharpExtractor/CSharpExtractor/Extractor/Extractor.cs b/CSharpExtractor/CSharpExtractor/Extractor/Extractor.cs
index 0184b25..98a9d03 100644
--- a/CSharpExtractor/CSharpExtractor/Extractor/Extractor.cs
+++ b/CSharpExtractor/CSharpExtractor/Extractor/Extractor.cs
@@ -6,6 +6,8 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
+using System.Diagnostics;
+
 
 namespace Extractor
 {
@@ -27,12 +29,14 @@ public class Extractor
         public int WidthLimit { get; set; }
         public string Code { get; set; }
         public bool ShouldHash { get; set; }
+        public int MaxContexts { get; set; }
 
-		public Extractor(string code, Options opts)
+        public Extractor(string code, Options opts)
 		{
             LengthLimit = opts.MaxLength;
             WidthLimit = opts.MaxWidth;
             ShouldHash = !opts.NoHash;
+            MaxContexts = opts.MaxContexts;
             Code = code;
 		}
 
@@ -104,29 +108,32 @@ private string PathToString(PathFinder.Path path)
 			return builder.ToString();
 		}
 
-		internal IEnumerable<PathFinder.Path> GetInternalPaths(Tree tree)
-		{
+        internal IEnumerable<PathFinder.Path> GetInternalPaths(Tree tree)
+        {
             var finder = new PathFinder(tree, LengthLimit, WidthLimit);
-            foreach (Tuple<Variable, Variable> varPair in 
-			         Utilities.WeakConcat(Utilities.Choose2(variables), 
-			                              variables.Select((arg) => new Tuple<Variable,Variable>(arg,arg))))
-			{
-				bool pathToSelf = varPair.Item1 == varPair.Item2;
-
-				foreach(var lhs in varPair.Item1.Leaves)
-				foreach (var rhs in varPair.Item2.Leaves)
-				{
-					if (lhs == rhs)
-							continue;
-					
-					PathFinder.Path path = finder.FindPath(lhs, rhs, limited: true);
-
-					if (path == null)
-						continue;
-                    
-
-					yield return path;
-				}
+
+            var allPairs = Utilities.ReservoirSample(Utilities.WeakConcat(Utilities.Choose2(variables),
+                         variables.Select((arg) => new Tuple<Variable, Variable>(arg, arg))), MaxContexts);
+
+            //iterate over variable-variable pairs
+            foreach (Tuple<Variable, Variable> varPair in allPairs)
+            {
+                bool pathToSelf = varPair.Item1 == varPair.Item2;
+
+                foreach (var rhs in varPair.Item2.Leaves)
+                    foreach (var lhs in varPair.Item1.Leaves)
+    				{
+                        
+                        if (lhs == rhs)
+    						continue;
+
+                        PathFinder.Path path = finder.FindPath(lhs, rhs, limited: true);
+
+    					if (path == null)
+    						continue;
+                            
+                        yield return path;
+    				}
 			}
 		}
 
@@ -167,6 +174,7 @@ public List<String> Extract()
             List<String> results = new List<string>();
 
             foreach(var method in methods) {
+
                 String methodName = method.Identifier.ValueText;
                 Tree methodTree = new Tree(method);
                 var subtokensMethodName = Utilities.SplitToSubtokens(methodName);
@@ -185,10 +193,12 @@ public List<String> Extract()
 
                 foreach (PathFinder.Path path in GetInternalPaths(methodTree))
                 {
-                    contexts.Add(SplitNameUnlessEmpty(tokenToVar[path.Left].Name)
+                    String pathString = SplitNameUnlessEmpty(tokenToVar[path.Left].Name)
                         + "," + MaybeHash(this.PathNodesToString(path))
-                        + "," + SplitNameUnlessEmpty(tokenToVar[path.Right].Name));
+                        + "," + SplitNameUnlessEmpty(tokenToVar[path.Right].Name);
 
+                    Debug.WriteLine(path.Left.FullSpan+" "+tokenToVar[path.Left].Name+ "," +this.PathNodesToString(path)+ "," + tokenToVar[path.Right].Name+" "+path.Right.FullSpan);    
+                    contexts.Add(pathString);
                 }
 
                 var commentNodes = tree.GetRoot().DescendantTrivia().Where(
@@ -206,7 +216,7 @@ public List<String> Extract()
                         contexts.Add(batch + "," + "COMMENT" + "," + batch);
                     }
                 }
-                results.Add(String.Join("|", subtokensMethodName) + " " + String.Join(" ", contexts));
+                results.Add(String.Join("|", subtokensMethodName) + " " + String.Join(" ", contexts));  
             }
             return results;
         }
diff --git a/CSharpExtractor/CSharpExtractor/Extractor/Program.cs b/CSharpExtractor/CSharpExtractor/Extractor/Program.cs
index c383301..d3b51d3 100644
--- a/CSharpExtractor/CSharpExtractor/Extractor/Program.cs
+++ b/CSharpExtractor/CSharpExtractor/Extractor/Program.cs
@@ -44,9 +44,12 @@ static void Main(string[] args)
 
             results = files.AsParallel().WithDegreeOfParallelism(options.Threads).SelectMany(filename => ExtractSingleFile(filename, options));
 
-            foreach (var res in results)
+            using (StreamWriter sw = new StreamWriter(options.OFileName, append: true))
             {
-                Console.WriteLine(res);
+                foreach (var res in results)
+                {
+                    sw.WriteLine(res);
+                }
             }
         }
     }
diff --git a/CSharpExtractor/CSharpExtractor/Extractor/Utilities.cs b/CSharpExtractor/CSharpExtractor/Extractor/Utilities.cs
index 4604fc9..666eec1 100644
--- a/CSharpExtractor/CSharpExtractor/Extractor/Utilities.cs
+++ b/CSharpExtractor/CSharpExtractor/Extractor/Utilities.cs
@@ -3,6 +3,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
+using System.Diagnostics;
 using System.Text.RegularExpressions;
 
 namespace Extractor
@@ -21,11 +22,17 @@ public class Options
         [Option('l', "max_width", Default = 2, HelpText = "Max path length")]
         public int MaxWidth { get; set; }
 
+        [Option('o', "ofile_name", Default = "test.txt", HelpText = "Output file name")]
+        public String OFileName { get; set; }
+
         [Option('h', "no_hash", Default = false, HelpText = "When enabled, prints the whole path strings (not hashed)")]
         public Boolean NoHash { get; set; }
+
+        [Option('l', "max_contexts", Default = 30000, HelpText = "Max number of path contexts to sample. Affects only very large snippets")]
+        public int MaxContexts { get; set; }
     }
 
-    public class Utilities
+    public static class Utilities
 	{
 	    public static String[] NumbericLiteralsToKeep = new String[] { "0", "1", "2", "3", "4", "5", "10" };
         public static IEnumerable<Tuple<T, T>> Choose2<T>(IEnumerable<T> enumerable)
@@ -40,7 +47,41 @@ public static IEnumerable<Tuple<T, T>> Choose2<T>(IEnumerable<T> enumerable)
 			}
 		}
 
-		public static IEnumerable<T> WeakConcat<T>(IEnumerable<T> enumerable1, IEnumerable<T> enumerable2)
+        /// <summary>
+        /// Sample uniform randomly numSamples from an enumerable, using reservoir sampling.
+        /// See https://en.wikipedia.org/wiki/Reservoir_sampling
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="input"></param>
+        /// <param name="numSamples"></param>
+        /// <returns></returns>
+        public static IEnumerable<TSource> ReservoirSample<TSource>(this IEnumerable<TSource> input, int numSamples)
+        {
+            var rng = new Random();
+            var sampledElements = new List<TSource>(numSamples);
+            int seenElementCount = 0;
+            foreach (var element in input)
+            {
+                seenElementCount++;
+                if (sampledElements.Count < numSamples)
+                {
+                    sampledElements.Add(element);
+                }
+                else
+                {
+                    int position = rng.Next(seenElementCount);
+                    if (position < numSamples)
+                    {
+                        sampledElements[position] = element;
+                    }
+                }
+            }
+            Debug.Assert(sampledElements.Count <= numSamples);
+            return sampledElements;
+        }
+
+
+        public static IEnumerable<T> WeakConcat<T>(IEnumerable<T> enumerable1, IEnumerable<T> enumerable2)
 		{
 			foreach (T t in enumerable1)
 				yield return t;
diff --git a/CSharpExtractor/CSharpExtractor/Extractor/Variable.cs b/CSharpExtractor/CSharpExtractor/Extractor/Variable.cs
index 0fe8ae3..ff94959 100644
--- a/CSharpExtractor/CSharpExtractor/Extractor/Variable.cs
+++ b/CSharpExtractor/CSharpExtractor/Extractor/Variable.cs
@@ -94,8 +94,15 @@ internal static IEnumerable<Variable> CreateFromMethod(Tree methodTree)
 					string name = tokenToName[leaf];
 					SyntaxToken[] syntaxTokens = nameToTokens[name].ToArray();
                     var v = new Variable(name, syntaxTokens, methodTree);
-                    results.Add(v);
-				}
+
+                    //check if exists
+                    var matches = results.Where(p => p.Name == name).ToList();
+                    bool alreadyExists = (matches.Count != 0);
+                    if (!alreadyExists)
+                    {
+                        results.Add(v);
+                    }
+                }
 
                 return results;
 			}
diff --git a/CSharpExtractor/extract.py b/CSharpExtractor/extract.py
index 104a881..f7a5d98 100644
--- a/CSharpExtractor/extract.py
+++ b/CSharpExtractor/extract.py
@@ -27,35 +27,30 @@ def ParallelExtractDir(args, dir):
 def ExtractFeaturesForDir(args, dir, prefix):
     command = ['dotnet', 'run', '--project', args.csproj,
                '--max_length', str(args.max_path_length), '--max_width', str(args.max_path_width),
-               '--path', dir, '--threads', str(args.num_threads)]
+               '--path', dir, '--threads', str(args.num_threads), '--ofile_name', str(args.ofile_name)]
+
 
     # print command
     # os.system(command)
     kill = lambda process: process.kill()
-    outputFileName = TMP_DIR + prefix + dir.split('/')[-1]
-    failed = False
-    with open(outputFileName, 'a') as outputFile:
-        sleeper = subprocess.Popen(command, stdout=outputFile, stderr=subprocess.PIPE)
-        timer = Timer(600000, kill, [sleeper])
-
-        try:
-            timer.start()
-            stdout, stderr = sleeper.communicate()
-        finally:
-            timer.cancel()
-
-        if sleeper.poll() == 0:
-            if len(stderr) > 0:
-                print(sys.stderr, stderr, file=sys.stdout)
-        else:
-            print(sys.stderr, 'dir: ' + str(dir) + ' was not completed in time', file=sys.stdout)
-            failed = True
-            subdirs = get_immediate_subdirectories(dir)
-            for subdir in subdirs:
-                ExtractFeaturesForDir(args, subdir, prefix + dir.split('/')[-1] + '_')
-    if failed:
-        if os.path.exists(outputFileName):
-            os.remove(outputFileName)
+    sleeper = subprocess.Popen(command, stderr=subprocess.PIPE)
+    timer = Timer(600000, kill, [sleeper])
+
+    try:
+        timer.start()
+        _, stderr = sleeper.communicate()
+    finally:
+        timer.cancel()
+
+    if sleeper.poll() == 0:
+        if len(stderr) > 0:
+            print(sys.stderr, stderr)
+    else:
+        print(sys.stderr, 'dir: ' + str(dir) + ' was not completed in time')
+        failed = True
+        subdirs = get_immediate_subdirectories(dir)
+        for subdir in subdirs:
+            ExtractFeaturesForDir(args, subdir, prefix + dir.split('/')[-1] + '_')
 
 
 def ExtractFeaturesForDirsList(args, dirs):
@@ -77,12 +72,14 @@ def ExtractFeaturesForDirsList(args, dirs):
 
 
 if __name__ == '__main__':
+
     parser = ArgumentParser()
     parser.add_argument("-maxlen", "--max_path_length", dest="max_path_length", required=False, default=8)
     parser.add_argument("-maxwidth", "--max_path_width", dest="max_path_width", required=False, default=2)
     parser.add_argument("-threads", "--num_threads", dest="num_threads", required=False, default=64)
     parser.add_argument("--csproj", dest="csproj", required=True)
     parser.add_argument("-dir", "--dir", dest="dir", required=False)
+    parser.add_argument("-ofile_name", "--ofile_name", dest="ofile_name", required=True)
     args = parser.parse_args()
 
     if args.dir is not None:
@@ -91,5 +88,3 @@ def ExtractFeaturesForDirsList(args, dirs):
         if len(subdirs) == 0:
             to_extract = [args.dir.rstrip('/')]
         ExtractFeaturesForDirsList(args, to_extract)
-
-
diff --git a/preprocess_csharp.sh b/preprocess_csharp.sh
index 54ec490..4a43105 100644
--- a/preprocess_csharp.sh
+++ b/preprocess_csharp.sh
@@ -39,13 +39,13 @@ mkdir -p data
 mkdir -p data/${DATASET_NAME}
 
 echo "Extracting paths from validation set..."
-${PYTHON} CSharpExtractor/extract.py --dir ${VAL_DIR} --max_path_length 8 --max_path_width 2 --num_threads ${NUM_THREADS} --csproj ${EXTRACTOR_JAR} > ${VAL_DATA_FILE}
+${PYTHON} CSharpExtractor/extract.py --dir ${VAL_DIR} --max_path_length 8 --max_path_width 2 --num_threads ${NUM_THREADS} --csproj ${EXTRACTOR_JAR} --ofile_name ${VAL_DATA_FILE}
 echo "Finished extracting paths from validation set"
 echo "Extracting paths from test set..."
-${PYTHON} CSharpExtractor/extract.py --dir ${TEST_DIR} --max_path_length 8 --max_path_width 2 --num_threads ${NUM_THREADS} --csproj ${EXTRACTOR_JAR} > ${TEST_DATA_FILE}
+${PYTHON} CSharpExtractor/extract.py --dir ${TEST_DIR} --max_path_length 8 --max_path_width 2 --num_threads ${NUM_THREADS} --csproj ${EXTRACTOR_JAR} --ofile_name ${TEST_DATA_FILE}
 echo "Finished extracting paths from test set"
 echo "Extracting paths from training set..."
-${PYTHON} CSharpExtractor/extract.py --dir ${TRAIN_DIR} --max_path_length 8 --max_path_width 2 --num_threads ${NUM_THREADS} --csproj ${EXTRACTOR_JAR} > ${TRAIN_DATA_FILE}
+${PYTHON} CSharpExtractor/extract.py --dir ${TRAIN_DIR} --max_path_length 8 --max_path_width 2 --num_threads ${NUM_THREADS} --csproj ${EXTRACTOR_JAR} --ofile_name ${TRAIN_DATA_FILE}
 echo "Finished extracting paths from training set"
 
 TARGET_HISTOGRAM_FILE=data/${DATASET_NAME}/${DATASET_NAME}.histo.tgt.c2v