Add WeightedList

- a utility class to encapsulate a list of data with associated weights for random selection.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@6705 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/main/java/com/threerings/util/WeightedList.java

@@ -0,0 +1,147 @@
+//
+// $Id$
+//
+// Narya library - tools for developing networked games
+// Copyright (C) 2002-2011 Three Rings Design, Inc., All Rights Reserved
+// http://code.google.com/p/narya/
+//
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.threerings.util;
+
+import java.util.List;
+import java.util.Random;
+
+import com.google.common.collect.Lists;
+
+import com.samskivert.util.RandomUtil;
+import com.samskivert.util.StringUtil;
+import com.samskivert.util.Tuple;
+
+public class WeightedList<T>
+{
+    public static <K> WeightedList<K> newList ()
+    {
+        return new WeightedList<K>();
+    }
+
+    public static <K> WeightedList<K> newList (K... entry)
+    {
+        return new WeightedList<K>().add(entry);
+    }
+
+    public static <K> WeightedList<K> newList (Float weight, K entry)
+    {
+        return new WeightedList<K>().add(weight, entry);
+    }
+
+    public static <K> WeightedList<K> newList (Float weight, K... entry)
+    {
+        return new WeightedList<K>().add(weight, entry);
+    }
+
+    /**
+     * Adds the given items with a weight of 1.
+     */
+    public WeightedList<T> add (T... items)
+    {
+        return add(1f, items);
+    }
+
+    /**
+     * Adds the given item with the given weight.
+     */
+    public WeightedList<T> add (float weight, T item)
+    {
+        _items.add(new Tuple<Float, T>(weight, item));
+        _weights = null;
+        return this;
+    }
+
+    /**
+     * Adds all of the given items with the given weight.
+     */
+    public WeightedList<T> add (float weight, T... items)
+    {
+        for (T item : items) {
+            add(weight, item);
+        }
+        return this;
+    }
+
+    /**
+     * Returns the weight for the first found instance of the given item,
+     * or -1 if we don't know about it.
+     */
+    public float getWeight (T item)
+    {
+        for (Tuple<Float, T> tup : _items) {
+            if (tup.right.equals(item)) {
+                return tup.left;
+            }
+        }
+
+        return -1;
+    }
+
+    /**
+     * Removes the record we have for this item at this weight.
+     */
+    public boolean remove (float weight, T item)
+    {
+        _weights = null;
+        return _items.remove(new Tuple<Float, T>(weight, item));
+    }
+
+    public T pickRandom ()
+    {
+        return pickRandom(RandomUtil.rand);
+    }
+
+    public T pickRandom (Random rand)
+    {
+        if (_weights == null) {
+            _weights = new float[_items.size()];
+
+            for (int ii = 0; ii < _weights.length; ii++) {
+                _weights[ii] = _items.get(ii).left;
+            }
+        }
+
+        int idx = RandomUtil.getWeightedIndex(_weights, rand);
+        return idx == -1 ? null : _items.get(idx).right;
+    }
+
+    public List<Tuple<Float, T>> getItems ()
+    {
+        return _items;
+    }
+
+    public int size ()
+    {
+        return _items.size();
+    }
+
+    @Override
+    public String toString ()
+    {
+        return StringUtil.toString(_items);
+    }
+
+    protected float[] _weights;
+
+    protected List<Tuple<Float, T>> _items = Lists.newArrayList();
+}
+