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Nix getWeighted() and rearrange the Map overload of pick().

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git-svn-id: https://samskivert.googlecode.com/svn/trunk@2918 6335cc39-0255-0410-8fd6-9bcaacd3b74c
This commit is contained in:
ray.j.greenwell
2010-10-13 19:48:05 +00:00
parent 1f0d6a4a3c
commit 003d8819ce
1 changed files with 28 additions and 58 deletions
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src/main/java/com/samskivert/util/Randoms.java
+28 -58
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@@ -142,64 +142,6 @@ public class Randoms
return (float)_r.nextGaussian() * dev + mean;
}
/**
* Pick a random key from the specified mapping of weight values, or return
* <code>ifEmpty</code> if no mapping 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 IllegalArgumentException if any weight is less than 0.
*/
public <T> T pick (Map<? extends T, ? extends Number> weightMap, T ifEmpty)
{
T pick = ifEmpty;
double total = 0.0;
for (Map.Entry<? extends T, ? extends Number> entry : weightMap.entrySet()) {
double weight = entry.getValue().doubleValue();
if (weight > 0.0) {
total += weight;
if ((total == weight) || ((_r.nextDouble() * total) < weight)) {
pick = entry.getKey();
}
} else if (weight < 0.0) {
throw new IllegalArgumentException("Weight less than 0: " + entry);
} // else: weight == 0.0 is OK
}
return pick;
}
/**
* Returns a key from the supplied map according to a probability computed as
* the key's value divided by the total of all the key's values.
*
* @throws NullPointerException if the map is null.
* @throws IllegalArgumentException if the sum of the weights is not positive.
*
* @deprecated Use {@link #pick(Map, Object)} instead.
*/
@Deprecated
public <T> T getWeighted (Map<T, ? extends Number> valuesToWeights)
{
// TODO: validate each weight to ensure it's not below 0
double sum = Folds.sum(0.0, valuesToWeights.values());
if (sum <= 0) {
throw new IllegalArgumentException("The sum of the weights is not positive");
}
// TODO: iterate all entries once, similarly to picking from an Iterable?
double d = _r.nextDouble() * sum;
for (Map.Entry<T, ? extends Number> entry : valuesToWeights.entrySet()) {
d -= entry.getValue().doubleValue();
if (d < 0) {
return entry.getKey();
}
}
// TODO: due to rounding error when iteratively subtract doubles, it might
// be possible to fall out of the loop here. Remember the highest-weighted entry
// and return it? (returning the last entry could be incorrect if it had a weight of 0).
throw new AssertionError("Not possible");
}
/**
* Pick a random element from the specified Iterator, or return <code>ifEmpty</code>
* if it is empty.
@@ -240,6 +182,34 @@ public class Randoms
return pickPluck(iterable, ifEmpty, false);
}
/**
* Pick a random <em>key</em> from the specified mapping of weight values, or return
* <code>ifEmpty</code> if no mapping has a weight greater than <code>0</code>. Each
* weight value is evaluated as a double.
*
* <p><b>Implementation note:</b> a random number is generated for every entry with a
* non-zero weight after the first such entry.
*
* @throws IllegalArgumentException if any weight is less than 0.
*/
public <T> T pick (Map<? extends T, ? extends Number> weightMap, T ifEmpty)
{
T pick = ifEmpty;
double total = 0.0;
for (Map.Entry<? extends T, ? extends Number> entry : weightMap.entrySet()) {
double weight = entry.getValue().doubleValue();
if (weight > 0.0) {
total += weight;
if ((total == weight) || ((_r.nextDouble() * total) < weight)) {
pick = entry.getKey();
}
} else if (weight < 0.0) {
throw new IllegalArgumentException("Weight less than 0: " + entry);
} // else: weight == 0.0 is OK
}
return pick;
}
/**
* Pluck (remove) a random element from the specified Iterable, or return <code>ifEmpty</code>
* if it is empty.