From 3a278b0673bb1aca794d33d1767209d9bc2c2a9b Mon Sep 17 00:00:00 2001
From: Anton Antonov <antononcube@gmail.com>
Date: Mon, 13 Feb 2017 23:59:40 -0500
Subject: [PATCH] Implemented randomChoice.

---
 .../TriesWithFrequencies/src/Experiments.java |  6 ++
 .../src/TrieFunctions.java                    | 93 ++++++++++++++++---
 2 files changed, 86 insertions(+), 13 deletions(-)

diff --git a/Java/TriesWithFrequencies/src/Experiments.java b/Java/TriesWithFrequencies/src/Experiments.java
index 1d3fd0c5..332e1007 100644
--- a/Java/TriesWithFrequencies/src/Experiments.java
+++ b/Java/TriesWithFrequencies/src/Experiments.java
@@ -149,6 +149,12 @@ public static void basic() {
         System.out.println( TrieFunctions.leafProbabilitiesJSON( pstrie ) );
         System.out.println();
 
+        System.out.println( "randomChoice :");
+        System.out.println( TrieFunctions.randomChoice( pstrie, true ) );
+        System.out.println();
+        System.out.println( TrieFunctions.randomChoice( pstrie, false ) );
+        System.out.println();
+
 
 //        sampleSeq = new ArrayList<String>() {{ add("ar"); add("as"); }};
 //        List< List<String> > sampleSeqList = new ArrayList<>();
diff --git a/Java/TriesWithFrequencies/src/TrieFunctions.java b/Java/TriesWithFrequencies/src/TrieFunctions.java
index 4e65f22e..6ca1181c 100644
--- a/Java/TriesWithFrequencies/src/TrieFunctions.java
+++ b/Java/TriesWithFrequencies/src/TrieFunctions.java
@@ -281,15 +281,17 @@ public static List<List<String>> mapPosition(Trie tr, List<List<String>> words)
         return res;
     }
 
+
     //! @description Retrieval of a sub-trie corresponding to a "word".
     //! @param tr a trie object
     //! @param word a list of strings
+    //! @param
     public static Trie retrieve(Trie tr, List<String> word) {
 
         if (word == null || word.isEmpty()) {
             return tr;
         } else {
-            if (tr.getChildren() == null) {
+            if (tr.getChildren() == null || tr.getChildren().isEmpty() ) {
                 return tr;
             }
             Trie pos = tr.getChildren().get(word.get(0));
@@ -301,16 +303,6 @@ public static Trie retrieve(Trie tr, List<String> word) {
         }
     }
 
-    //! @description Optimization of retrieve over a list of words.
-    //! @param tr a trie object
-    //! @param words a list of lists of strings
-    public static List<Trie> mapRetrieve(Trie tr, List<List<String>> words) {
-        List<Trie> res = new ArrayList<>();
-        for (List<String> s : words) {
-            res.add(retrieve(tr, s));
-        }
-        return res;
-    }
 
     //! @description For a given trie finds if the retrievable part of a word is complete match.
     //! @param tr a trie object
@@ -698,7 +690,7 @@ public static List<Integer> nodeCounts(Trie tr) {
         Pair<Integer, Integer> res = nodeCountsRec(tr, 0, 0);
 
         return new ArrayList<Integer>()
-           {{ add(res.getKey() + res.getValue()); add(res.getKey()); add(res.getValue()); }};
+        {{ add(res.getKey() + res.getValue()); add(res.getKey()); add(res.getValue()); }};
     }
 
     //! @description Finding the counts of internal nodes and leaf nodes in a trie.
@@ -804,7 +796,7 @@ public static Trie map( Trie tr,  TrieNodeFunction preFunc, TrieNodeFunction pos
                 res = tr;
             }
 
-            if ( tr.getChildren() == null || tr.getChildren().isEmpty()) {
+            if ( res.getChildren() == null || res.getChildren().isEmpty()) {
 
                 resChildren = null;
 
@@ -1063,4 +1055,79 @@ public static Trie removeByParetoFraction( Trie tr, double paretoFraction, boole
 
         return map( tr, removalObj, null );
     }
+
+    ///**************************************************************
+    /// Random choice functions
+    ///**************************************************************
+
+    private static class ChildRandomChoice implements TrieNodeFunction {
+        ChildRandomChoice( boolean wsQ ) { weightedQ = wsQ; keyPath = new ArrayList(); }
+
+        public boolean weightedQ;
+        public List<String> keyPath;
+
+        private Trie randomSelection( Collection<Trie> children ) {
+
+            // Compute the total weight of all items together
+            double totalWeight = 0.0d;
+            if ( weightedQ ) {
+                for (Trie elem : children) {
+                    totalWeight += elem.getValue();
+                }
+            } else {
+                for (Trie elem : children) {
+                    totalWeight += 1.0;
+                }
+            }
+            // Now choose a random trie
+            Trie randomTrie = null;
+            double random = Math.random() * totalWeight;
+            int i = 0;
+            for ( Trie elem : children ) {
+                random -= elem.getValue();
+                if( randomTrie == null ) { randomTrie = elem; }
+                if (random <= 0.0d) {
+                    randomTrie = elem;
+                    break;
+                }
+                i++;
+            }
+
+            return randomTrie;
+        }
+
+        public Trie apply( Trie tr ) {
+
+            keyPath.add( tr.getKey() );
+
+            if( tr.getChildren() == null || tr.getChildren().isEmpty() ) {
+                return tr.clone();
+            } else {
+
+                Trie res = new Trie( tr.getKey(), tr.getValue() );
+                Trie sel = randomSelection( tr.getChildren().values() );
+
+                Map<String,Trie> resChildren = new HashMap();
+                resChildren.put( sel.getKey(), sel );
+                res.setChildren( resChildren );
+
+                return res;
+            }
+        }
+    }
+
+
+    //! @description Random choice of a root-to-leaf path.
+    //! @param tr a trie object
+    //! @param weightedQ should a weighted random choice be used or not
+    public static List<String> randomChoice( Trie tr, boolean weightedQ ) {
+
+        ChildRandomChoice selectObj = new ChildRandomChoice( weightedQ );
+
+        Trie res = map( tr, selectObj, null );
+
+        return selectObj.keyPath;
+    }
+
+
 }
\ No newline at end of file