AfflictionNetworks/samskivert
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What was I thinking?: we can't just pick a random number once.

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Unsmoke that crack.


git-svn-id: https://samskivert.googlecode.com/svn/trunk@2916 6335cc39-0255-0410-8fd6-9bcaacd3b74c
This commit is contained in:
ray.j.greenwell
2010-10-13 00:12:50 +00:00
parent 5a8ee16ec5
commit 3dadbe13b9
1 changed files with 4 additions and 2 deletions
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src/main/java/com/samskivert/util/Randoms.java
+4 -2
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@@ -146,18 +146,20 @@ public class Randoms
* Pick a random key from the specified mapping of weight values, or return * Pick a random key from the specified mapping of weight values, or return
* <code>ifEmpty</code> if no mapping has a weight greater than 0. * <code>ifEmpty</code> if no mapping has a weight greater than 0.
* *
* <p><b>Implementation note:</b> a random number is generated for every entry with a
* non-zero weight.
*
* @throws IllegalArgumentException if any weight is less than 0. * @throws IllegalArgumentException if any weight is less than 0.
*/ */
public <T> T pick (Map<? extends T, ? extends Number> weightMap, T ifEmpty) public <T> T pick (Map<? extends T, ? extends Number> weightMap, T ifEmpty)
{ {
T pick = ifEmpty; T pick = ifEmpty;
double r = _r.nextDouble();
double total = 0.0; double total = 0.0;
for (Map.Entry<? extends T, ? extends Number> entry : weightMap.entrySet()) { for (Map.Entry<? extends T, ? extends Number> entry : weightMap.entrySet()) {
double weight = entry.getValue().doubleValue(); double weight = entry.getValue().doubleValue();
if (weight > 0.0) { if (weight > 0.0) {
total += weight; total += weight;
if ((r * total) < weight) { if ((_r.nextDouble() * total) < weight) {
pick = entry.getKey(); pick = entry.getKey();
} }
} else if (weight < 0.0) { } else if (weight < 0.0) {