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Added Weigher interface, and a pick(Iterable, Weigher).

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I wanted something like this before, but with guava's Function,
and samskivert doesn't depend have dependencies.
But with Java 8 coming, functional interfaces make the distinction
between different interfaces less important.
This commit is contained in:
Ray J. Greenwell
2014-04-23 10:08:18 -07:00
parent 2f4bdb961b
commit 66e0874633
1 changed files with 54 additions and 29 deletions
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src/main/java/com/samskivert/util/Randoms.java
+54 -29
View File
@@ -49,6 +49,17 @@ public class Randoms
return _localRandoms.get();
}
/**
* An interface for weighing pickable elements.
*/
public interface Weigher<T>
{
/**
* Get the weight of the specified value.
*/
public double getWeight (T value);
}
/**
* Returns a pseudorandom, uniformly distributed <code>int</code> value between <code>0</code>
* (inclusive) and <code>high</code> (exclusive).
@@ -208,47 +219,61 @@ public class Randoms
* @throws IllegalArgumentException if any weight is less than 0.
*/
public <T> T pick (Map<? extends T, ? extends Number> weightMap, T ifEmpty)
{
Map.Entry<? extends T, ? extends Number> pick = pick(
weightMap.entrySet(), null, new Weigher<Map.Entry<?, ? extends Number>>() {
public double getWeight (Map.Entry<?, ? extends Number> entry) {
return entry.getValue().doubleValue();
}
});
return (pick == null) ? ifEmpty : pick.getKey();
}
/**
* Pick a random element from the specified iterable, or return
* <code>ifEmpty</code> if no element has a weight greater than <code>0</code>.
*
* <p><b>Implementation note:</b> a random number is generated for every entry with a
* non-zero weight after the first such entry.
*
* @throws NullPointerException if values is null.
* @throws IllegalArgumentException if any weight is less than 0.
*/
public <T> T pick (Iterable<? extends T> values, T ifEmpty, Weigher<? super T> weigher)
{
return pick(values.iterator(), ifEmpty, weigher);
}
/**
* Pick a random element from the specified iterator, or return
* <code>ifEmpty</code> if no element has a weight greater than <code>0</code>.
*
* <p><b>Implementation note:</b> a random number is generated for every entry with a
* non-zero weight after the first such entry.
*
* @throws NullPointerException if values is null.
* @throws IllegalArgumentException if any weight is less than 0.
*/
public <T> T pick (Iterator<? extends T> values, T ifEmpty, Weigher<? super T> weigher)
{
T pick = ifEmpty;
double total = 0.0;
for (Map.Entry<? extends T, ? extends Number> entry : weightMap.entrySet()) {
double weight = entry.getValue().doubleValue();
while (values.hasNext()) {
T val = values.next();
double weight = weigher.getWeight(val);
if (weight > 0.0) {
total += weight;
if ((total == weight) || ((_r.nextDouble() * total) < weight)) {
pick = entry.getKey();
pick = val;
}
} else if (weight < 0.0) {
throw new IllegalArgumentException("Weight less than 0: " + entry);
} // else: weight == 0.0 is OK
throw new IllegalArgumentException("Weight less than 0: " + val);
}
// else: weight == 0.0 is OK
}
return pick;
}
// public <T> T pick (
// Iterable<? extends T> iterable, Function<? super T, ? extends Number> weightFunction,
// T ifEmpty)
// {
// T pick = ifEmpty;
// double total = 0.0;
// for (T element : iterable) {
// double weight = weightFunction.apply(element).doubleValue();
// // The rest is like the current pick(Map)
// }
// return pick;
// }
//
// public <T> T pick (Map<? extends T, ? extends Number> weightMap, T ifEmpty)
// {
// Map.Entry<? extends T, ? extends Number> pick = pick(weightMap.entrySet(),
// new Function<Map.Entry<?, ? extends Number>, Number>() {
// public Number apply (Map.Entry<?, ? extends Number> entry) {
// return entry.getValue();
// }
// }, null);
// return (pick != null) ? pick.getKey() : ifEmpty;
// }
/**
* Pluck (remove) a random element from the specified Iterable, or return <code>ifEmpty</code>
* if it is empty.