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Core sketch algorithms used alone and by other Java repositories in the DataSketches library.
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
*/
package org.apache.datasketches.sampling;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* This class provides access to the samples contained in a VarOptItemsSketch. It provides two
* mechanisms for access:
*
* - An Iterator over WeightedSample objects which can can be used to
* access both the items and weights in the sample, and which avoids copying data from the
* sketch.
* - Getter methods to obtain items or weights as arrays, or individual items. These
* methods create a (shallow) copy of data from the sketch on the first call to any get
* method.
*
*
* If using getters with a sketch storing heterogeneous items from a polymorphic base class, you
* must call setClass() prior to calling one of the getter methods. This is not
* necessary if using the iterator.
*
* The class also implements Iterable to allow the use of forEach loops for
* convenience.
*
* @param an item of type T
*
* @author Jon Malkin
*/
public class VarOptItemsSamples implements Iterable.WeightedSample> {
private final VarOptItemsSketch sketch_;
private VarOptItemsSketch.Result sampleLists;
private final long n_;
private final int h_;
private final double rWeight_;
/**
* A convenience class to allow easy iterator access to a VarOpt sample.
*/
public final class WeightedSample {
private final int idx_;
private double adjustedWeight_;
private WeightedSample(final int i) {
idx_ = i;
adjustedWeight_ = Double.NaN;
}
private WeightedSample(final int i, final double adjustedWeight) {
idx_ = i;
adjustedWeight_ = adjustedWeight;
}
/**
* Accesses the iterator's current object
* @return An item from the sketch's data sample
*/
public T getItem() {
return sketch_.getItem(idx_);
}
/**
* Accesses the iterator's current weight value
* @return A weight from the sketch's data sample
*/
public double getWeight() {
if (idx_ > h_) {
return Double.isNaN(adjustedWeight_) ? rWeight_ : adjustedWeight_;
} else {
return sketch_.getWeight(idx_);
}
}
// only used in resolving union gadget
boolean getMark() { return sketch_.getMark(idx_); }
}
/**
* The standard iterator
*/
public class VarOptItemsIterator implements Iterator {
int currIdx_;
int finalIdx_; // inclusive final index
VarOptItemsIterator() {
currIdx_ = h_ == 0 ? 1 : 0;
final int k = sketch_.getK();
finalIdx_ = (int) (n_ <= k ? n_ - 1 : k); // -1 since finalIdx_ is inclusive
}
// package private iterator to crawl only H or only R region values
VarOptItemsIterator(final boolean useRRegion) {
if (useRRegion) {
currIdx_ = h_ + 1; // to handle the gap
finalIdx_ = sketch_.getNumSamples(); // no +1 since inclusive
} else {
currIdx_ = 0;
finalIdx_ = h_ - 1; // need stop before h_ since incluside
}
}
@Override
public boolean hasNext() {
// If sketch is in exact mode, we'll have a next item as long as index < k.
// If in sampling mode, the last index is k (array length k+1) but there will always be at
// least one item in R, so no need to check if the last element is null.
return currIdx_ <= finalIdx_;
}
@Override
public WeightedSample next() {
if (n_ != sketch_.getN()) {
throw new ConcurrentModificationException();
} else if (currIdx_ > finalIdx_) {
throw new NoSuchElementException();
}
// grab current index, apply logic to update currIdx_ for the next call
final int tgt = currIdx_;
++currIdx_;
if ((currIdx_ == h_) && (h_ != n_)) {
++currIdx_;
}
return new WeightedSample(tgt);
}
}
class WeightCorrectingRRegionIterator extends VarOptItemsIterator {
private double cumWeight = 0.0;
WeightCorrectingRRegionIterator() {
super(true);
}
@Override
public WeightedSample next() {
if (n_ != sketch_.getN()) {
throw new ConcurrentModificationException();
} else if (currIdx_ > finalIdx_) {
throw new NoSuchElementException();
}
// grab current index, apply logic to update currIdx_ for the next call
final int tgt = currIdx_;
++currIdx_;
// only covers R region, no need to check for gap
final WeightedSample sample;
if (tgt == finalIdx_) {
sample = new WeightedSample(tgt, sketch_.getTotalWtR() - cumWeight);
} else {
sample = new WeightedSample(tgt);
cumWeight += rWeight_;
}
return sample;
}
}
VarOptItemsSamples(final VarOptItemsSketch sketch) {
sketch_ = sketch;
n_ = sketch.getN();
h_ = sketch.getHRegionCount();
rWeight_ = sketch.getTau();
}
@Override
public Iterator iterator() {
return new VarOptItemsIterator();
}
Iterator getHIterator() { return new VarOptItemsIterator(false); }
Iterator getRIterator() { return new VarOptItemsIterator(true); }
Iterator getWeightCorrRIter() { return new WeightCorrectingRRegionIterator(); }
/**
* Specifies the class to use when copying the item array from the sketch. This method is
* required if the sketch stores heterogeneous item types of some base class, for instance a
* sketch over Numbers.
*
* @param clazz The class to use when creating the item array result
*/
public void setClass(final Class clazz) {
if (sampleLists == null) {
sampleLists = sketch_.getSamplesAsArrays(clazz);
}
}
/**
* Returns the length Copies items and weights from the sketch, if necessary, and returns the
* length of
* any
* resulting array. The result will be 0 for an empty sketch.
*
* @return The number of items and weights in the sketch
*/
public int getNumSamples() {
loadArrays();
return (sampleLists == null ? 0 : sampleLists.weights.length);
}
/**
* Returns a shallow copy of the array of sample items contained in the sketch. If this is the
* first getter call, copies data arrays from the sketch.
* @return The number of samples contained in the sketch.
*/
public T[] items() {
loadArrays();
return (sampleLists == null ? null : sampleLists.items);
}
/**
* Returns a single item from the samples contained in the sketch. Does not perform bounds
* checking on the input. If this is the first getter call, copies data arrays from the sketch.
* @param i An index into the list of samples
* @return The sample at array position i
*/
public T items(final int i) {
loadArrays();
return (sampleLists == null ? null : sampleLists.items[i]);
}
/**
* Returns a copy of the array of weights contained in the sketch. If this is the first
* getter call, copies data arrays from the sketch.
* @return The number of samples contained in the sketch.
*/
public double[] weights() {
loadArrays();
return (sampleLists == null ? null : sampleLists.weights);
}
/**
* Returns a single weight from the samples contained in the sketch. Does not perform bounds
* checking on the input. If this is the first getter call, copies data arrays from the sketch.
* @param i An index into the list of weights
* @return The weight at array position i
*/
public double weights(final int i) {
loadArrays();
return (sampleLists == null ? Double.NaN : sampleLists.weights[i]);
}
private void loadArrays() {
if (sampleLists == null) {
sampleLists = sketch_.getSamplesAsArrays();
}
}
}
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