Frequency.java
/*
* 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.commons.math4.legacy.stat;
import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.SortedMap;
import java.util.TreeMap;
import org.apache.commons.math4.legacy.exception.NullArgumentException;
import org.apache.commons.math4.legacy.exception.util.LocalizedFormats;
/**
* Maintains a frequency distribution.
*
* <p>The values are ordered using the default (natural order), unless a
* <code>Comparator</code> is supplied in the constructor.</p>
*
* @param <T> a comparable type used in the frequency distribution
*/
public class Frequency<T extends Comparable<T>> {
/** underlying collection. */
private final SortedMap<T, Long> freqTable;
/**
* Default constructor.
*/
public Frequency() {
freqTable = new TreeMap<>();
}
/**
* Constructor allowing values Comparator to be specified.
*
* @param comparator Comparator used to order values
*/
public Frequency(Comparator<T> comparator) {
freqTable = new TreeMap<>(comparator);
}
/**
* Return a string representation of this frequency distribution.
*
* @return a string representation.
*/
@Override
public String toString() {
NumberFormat nf = NumberFormat.getPercentInstance();
StringBuilder outBuffer = new StringBuilder();
outBuffer.append("Value \t Freq. \t Pct. \t Cum Pct. \n");
Iterator<T> iter = freqTable.keySet().iterator();
while (iter.hasNext()) {
T value = iter.next();
outBuffer.append(value);
outBuffer.append('\t');
outBuffer.append(getCount(value));
outBuffer.append('\t');
outBuffer.append(nf.format(getPct(value)));
outBuffer.append('\t');
outBuffer.append(nf.format(getCumPct(value)));
outBuffer.append('\n');
}
return outBuffer.toString();
}
/**
* Adds 1 to the frequency count for v.
*
* @param v the value to add.
*/
public void addValue(T v) {
incrementValue(v, 1);
}
/**
* Increments the frequency count for v.
*
* @param v the value to add.
* @param increment the amount by which the value should be incremented
* @since 3.1
*/
public void incrementValue(T v, long increment) {
Long count = freqTable.get(v);
if (count == null) {
freqTable.put(v, Long.valueOf(increment));
} else {
freqTable.put(v, Long.valueOf(count.longValue() + increment));
}
}
/** Clears the frequency table. */
public void clear() {
freqTable.clear();
}
/**
* Returns an Iterator over the set of values that have been added.
*
* @return values Iterator
*/
public Iterator<T> valuesIterator() {
return freqTable.keySet().iterator();
}
/**
* Return an Iterator over the set of keys and values that have been added.
* Using the entry set to iterate is more efficient in the case where you
* need to access respective counts as well as values, since it doesn't
* require a "get" for every key...the value is provided in the Map.Entry.
*
* @return entry set Iterator
* @since 3.1
*/
public Iterator<Map.Entry<T, Long>> entrySetIterator() {
return freqTable.entrySet().iterator();
}
//-------------------------------------------------------------------------
/**
* Returns the sum of all frequencies.
*
* @return the total frequency count.
*/
public long getSumFreq() {
long result = 0;
Iterator<Long> iterator = freqTable.values().iterator();
while (iterator.hasNext()) {
result += iterator.next().longValue();
}
return result;
}
/**
* Returns the number of values equal to v.
*
* @param v the value to lookup.
* @return the frequency of v.
*/
public long getCount(T v) {
long result = 0;
Long count = freqTable.get(v);
if (count != null) {
result = count.longValue();
}
return result;
}
/**
* Returns the number of values in the frequency table.
*
* @return the number of unique values that have been added to the frequency table.
* @see #valuesIterator()
*/
public int getUniqueCount(){
return freqTable.keySet().size();
}
/**
* Returns the percentage of values that are equal to v
* (as a proportion between 0 and 1).
* <p>
* Returns <code>Double.NaN</code> if no values have been added.
* </p>
*
* @param v the value to lookup
* @return the proportion of values equal to v
*/
public double getPct(T v) {
final long sumFreq = getSumFreq();
if (sumFreq == 0) {
return Double.NaN;
}
return (double) getCount(v) / (double) sumFreq;
}
//-----------------------------------------------------------------------------------------
/**
* Returns the cumulative frequency of values less than or equal to v.
*
* @param v the value to lookup.
* @return the proportion of values equal to v
*/
public long getCumFreq(T v) {
if (getSumFreq() == 0) {
return 0;
}
Comparator<? super T> c = freqTable.comparator();
if (c == null) {
c = new NaturalComparator<>();
}
long result = 0;
Long value = freqTable.get(v);
if (value != null) {
result = value.longValue();
}
if (c.compare(v, freqTable.firstKey()) < 0) {
return 0; // v is comparable, but less than first value
}
if (c.compare(v, freqTable.lastKey()) >= 0) {
return getSumFreq(); // v is comparable, but greater than the last value
}
Iterator<T> values = valuesIterator();
while (values.hasNext()) {
T nextValue = values.next();
if (c.compare(v, nextValue) > 0) {
result += getCount(nextValue);
} else {
return result;
}
}
return result;
}
//----------------------------------------------------------------------------------------------
/**
* Returns the cumulative percentage of values less than or equal to v
* (as a proportion between 0 and 1).
* <p>
* Returns <code>Double.NaN</code> if no values have been added.
* </p>
*
* @param v the value to lookup
* @return the proportion of values less than or equal to v
*/
public double getCumPct(T v) {
final long sumFreq = getSumFreq();
if (sumFreq == 0) {
return Double.NaN;
}
return (double) getCumFreq(v) / (double) sumFreq;
}
/**
* Returns the mode value(s) in comparator order.
*
* @return a list containing the value(s) which appear most often.
* @since 3.3
*/
public List<T> getMode() {
long mostPopular = 0; // frequencies are always positive
// Get the max count first, so we avoid having to recreate the List each time
for(Long l : freqTable.values()) {
long frequency = l.longValue();
if (frequency > mostPopular) {
mostPopular = frequency;
}
}
List<T> modeList = new ArrayList<>();
for (Entry<T, Long> ent : freqTable.entrySet()) {
long frequency = ent.getValue().longValue();
if (frequency == mostPopular) {
modeList.add(ent.getKey());
}
}
return modeList;
}
//----------------------------------------------------------------------------------------------
/**
* Merge another Frequency object's counts into this instance.
* This Frequency's counts will be incremented (or set when not already set)
* by the counts represented by other.
*
* @param other the other {@link Frequency} object to be merged
* @throws NullArgumentException if {@code other} is null
* @since 3.1
*/
public void merge(final Frequency<T> other) throws NullArgumentException {
NullArgumentException.check(other, LocalizedFormats.NULL_NOT_ALLOWED);
final Iterator<Map.Entry<T, Long>> iter = other.entrySetIterator();
while (iter.hasNext()) {
final Map.Entry<T, Long> entry = iter.next();
incrementValue(entry.getKey(), entry.getValue().longValue());
}
}
/**
* Merge a {@link Collection} of {@link Frequency} objects into this instance.
* This Frequency's counts will be incremented (or set when not already set)
* by the counts represented by each of the others.
*
* @param others the other {@link Frequency} objects to be merged
* @throws NullArgumentException if the collection is null
* @since 3.1
*/
public void merge(final Collection<Frequency<T>> others) throws NullArgumentException {
NullArgumentException.check(others, LocalizedFormats.NULL_NOT_ALLOWED);
for (final Frequency<T> freq : others) {
merge(freq);
}
}
//----------------------------------------------------------------------------------------------
/**
* A Comparator that compares comparable objects using the
* natural order. Copied from Commons Collections ComparableComparator.
*
* @param <U> the type of the objects compared
*/
private static final class NaturalComparator<U extends Comparable<U>> implements Comparator<U> {
/**
* Compare the two {@link Comparable Comparable} arguments.
* This method is equivalent to:
* <pre>(({@link Comparable Comparable})o1).{@link Comparable#compareTo compareTo}(o2)</pre>
*
* @param o1 the first object
* @param o2 the second object
* @return result of comparison
* @throws NullPointerException when <i>o1</i> is <code>null</code>,
* or when <code>((Comparable)o1).compareTo(o2)</code> does
*/
@Override
public int compare(U o1, U o2) {
return o1.compareTo(o2);
}
}
/** {@inheritDoc} */
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result +
((freqTable == null) ? 0 : freqTable.hashCode());
return result;
}
/** {@inheritDoc} */
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (!(obj instanceof Frequency<?>)) {
return false;
}
Frequency<?> other = (Frequency<?>) obj;
return freqTable.equals(other.freqTable);
}
}