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DiscreteGenerator.java
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Mon, Aug 26, 01:43

DiscreteGenerator.java
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/**
* Copyright (c) 2010 Yahoo! Inc. All rights reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you
* may not use this file except in compliance with the License. You
* may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
* implied. See the License for the specific language governing
* permissions and limitations under the License. See accompanying
* LICENSE file.
*/
package com.yahoo.ycsb.generator;
import java.util.ArrayList;
import java.util.Collection;
import static java.util.Objects.requireNonNull;
import com.yahoo.ycsb.Utils;
/**
* Generates a distribution by choosing from a discrete set of values.
*/
public class DiscreteGenerator extends Generator<String>
{
private static class Pair
{
private double _weight;
private String _value;
Pair(double weight, String value)
{
_weight=weight;
_value = requireNonNull(value);
}
}
private final Collection<Pair> _values = new ArrayList<>();
private String _lastvalue;
public DiscreteGenerator()
{
_lastvalue=null;
}
/**
* Generate the next string in the distribution.
*/
@Override
public String nextValue()
{
double sum=0;
for (Pair p : _values)
{
sum+=p._weight;
}
double val=Utils.random().nextDouble();
for (Pair p : _values)
{
double pw = p._weight / sum;
if (val < pw)
{
return p._value;
}
val -= pw;
}
throw new AssertionError("oops. should not get here.");
}
/**
* Return the previous string generated by the distribution; e.g., returned from the last nextString() call.
* Calling lastString() should not advance the distribution or have any side effects. If nextString() has not yet
* been called, lastString() should return something reasonable.
*/
@Override
public String lastValue()
{
if (_lastvalue==null)
{
_lastvalue=nextValue();
}
return _lastvalue;
}
public void addValue(double weight, String value)
{
_values.add(new Pair(weight,value));
}
}

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