[ http://issues.apache.org/jira/browse/LUCENE691?page=all ]
Otis Gospodnetic updated LUCENE691:

Summary: Bob Carpenter's FuzzyTermEnum refactoring (was: Bob Carpenter's FuzzyQuery refactoring)
> Bob Carpenter's FuzzyTermEnum refactoring
> 
>
> Key: LUCENE691
> URL: http://issues.apache.org/jira/browse/LUCENE691
> Project: Lucene  Java
> Issue Type: Improvement
> Components: Search
> Reporter: Otis Gospodnetic
> Priority: Minor
>
> I'll just paste Bob's complete email here.
> I refactored the org.apache.lucene.search.FuzzyTermEnum
> edit distance implementation. It now only uses a single
> pair of arrays, and those never get resized. That required
> turning the order of text/target around in the loops. You'll
> see that with the pair of arrays method, they get reused
> handoverhand, and are assigned to local variables in the
> tight loops.
> I removed the calculation of min distance and replaced
> it with a boolean  the min wasn't needed, only the test vs.
> the max. I also flipped some variables around so there's
> one less addition in the very inner loop and the arrays are
> now looping in the ordinary way (starting at 0 with a < comparison).
> I also commented out the redundant definition of the public close()
> [which just called super.close() and had none of its own doc.]
> I also just compute the max distance each time rather than
> fiddling with an array  it's just a little arithmetic done once
> per term, but that could be put back.
> I also rewrote min(int,int,int) to get rid of intermediate
> assignments. Is there a lib for this kind of thing?
> An intermediate refactoring that does the handoverhand
> with the existing array and resizing strategy is in
> FuzzyTermEnum.intermed.java.
> I ran the unit tests as follows on both versions (my hat's off to the
> build.xml author(s)  this all just worked out of the box and was
> really easy to follow the first through):
> C:\java\lucene2.0.0>ant Djunit.includes="" Dtestcase=TestFuzzyQuery test
> Buildfile: build.xml
> javaccuptodatecheck:
> javaccnotice:
> init:
> common.compilecore:
> [javac] Compiling 1 source file to
> C:\java\lucene2.0.0\build\classes\java
> compilecore:
> compiledemo:
> common.compiletest:
> compiletest:
> test:
> [junit] Testsuite: org.apache.lucene.search.TestFuzzyQuery
> [junit] Tests run: 2, Failures: 0, Errors: 0, Time elapsed: 0.453 sec
> BUILD SUCCESSFUL
> Total time: 2 seconds
> Does anyone have regression/performance test harnesses?
> The unit tests were pretty minimal (which is a good thing!).
> It'd be nice to test the min impl (ternary vs. if/then)
> and the assumption about not allocating an
> array of max distances. All told, the refactored version
> should be a modest speed improvement, mainly from
> unfolding the arrays so they're local onedimensional refs.
> I don't know what the protocol is for oneoff contributions.
> I'm happy with the Apache license, so that shouldn't
> be a problem. I also don't know whether you use tabs
> or spaces  I untabified the final version and used your
> twospace format in emacs.
>  Bob Carpenter
> package org.apache.lucene.search;
> /**
> * Copyright 2004 The Apache Software Foundation
> *
> * 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/LICENSE2.0
> *
> * 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.
> */
> import org.apache.lucene.index.IndexReader;
> import org.apache.lucene.index.Term;
> import java.io.IOException;
> /** Subclass of FilteredTermEnum for enumerating all terms that are similiar
> * to the specified filter term.
> *
> * <p>Term enumerations are always ordered by Term.compareTo(). Each term in
> * the enumeration is greater than all that precede it.
> */
> public final class FuzzyTermEnum extends FilteredTermEnum {
> /* This should be somewhere around the average long word.
> * If it is longer, we waste time and space. If it is shorter, we waste a
> * little bit of time growing the array as we encounter longer words.
> */
> private static final int TYPICAL_LONGEST_WORD_IN_INDEX = 19;
> /* Allows us save time required to create a new array
> * everytime similarity is called. These are slices that
> * will be reused during dynamic programming handoverhand
> * style.
> */
> private final int[] d0;
> private final int[] d1;
> private float similarity;
> private boolean endEnum = false;
> private Term searchTerm = null;
> private final String field;
> private final String text;
> private final String prefix;
> private final float minimumSimilarity;
> private final float scale_factor;
> /**
> * Creates a FuzzyTermEnum with an empty prefix and a minSimilarity of 0.5f.
> * <p>
> * After calling the constructor the enumeration is already pointing to the first
> * valid term if such a term exists.
> *
> * @param reader
> * @param term
> * @throws IOException
> * @see #FuzzyTermEnum(IndexReader, Term, float, int)
> */
> public FuzzyTermEnum(IndexReader reader, Term term) throws IOException {
> this(reader, term, FuzzyQuery.defaultMinSimilarity, FuzzyQuery.defaultPrefixLength);
> }
>
> /**
> * Creates a FuzzyTermEnum with an empty prefix.
> * <p>
> * After calling the constructor the enumeration is already pointing to the first
> * valid term if such a term exists.
> *
> * @param reader
> * @param term
> * @param minSimilarity
> * @throws IOException
> * @see #FuzzyTermEnum(IndexReader, Term, float, int)
> */
> public FuzzyTermEnum(IndexReader reader, Term term, float minSimilarity) throws IOException
{
> this(reader, term, minSimilarity, FuzzyQuery.defaultPrefixLength);
> }
>
> /**
> * Constructor for enumeration of all terms from specified <code>reader</code>
which share a prefix of
> * length <code>prefixLength</code> with <code>term</code>
and which have a fuzzy similarity >
> * <code>minSimilarity</code>.
> * <p>
> * After calling the constructor the enumeration is already pointing to the first
> * valid term if such a term exists.
> *
> * @param reader Delivers terms.
> * @param term Pattern term.
> * @param minSimilarity Minimum required similarity for terms from the reader. Default
value is 0.5f.
> * @param prefixLength Length of required common prefix. Default value is 0.
> * @throws IOException
> */
> public FuzzyTermEnum(IndexReader reader, Term term, final float minSimilarity, final
int prefixLength) throws IOException {
> super();
>
> if (minSimilarity >= 1.0f)
> throw new IllegalArgumentException("minimumSimilarity cannot be greater than or
equal to 1");
> else if (minSimilarity < 0.0f)
> throw new IllegalArgumentException("minimumSimilarity cannot be less than 0");
> if(prefixLength < 0)
> throw new IllegalArgumentException("prefixLength cannot be less than 0");
> this.minimumSimilarity = minSimilarity;
> this.scale_factor = 1.0f / (1.0f  minimumSimilarity);
> this.searchTerm = term;
> this.field = searchTerm.field();
> //The prefix could be longer than the word.
> //It's kind of silly though. It means we must match the entire word.
> final int fullSearchTermLength = searchTerm.text().length();
> final int realPrefixLength = prefixLength > fullSearchTermLength ? fullSearchTermLength
: prefixLength;
> this.text = searchTerm.text().substring(realPrefixLength);
> this.prefix = searchTerm.text().substring(0, realPrefixLength);
> this.d0 = new int[this.text.length()+1];
> this.d1 = new int[this.d0.length];
> setEnum(reader.terms(new Term(searchTerm.field(), prefix)));
> }
> /**
> * The termCompare method in FuzzyTermEnum uses Levenshtein distance to
> * calculate the distance between the given term and the comparing term.
> */
> protected final boolean termCompare(Term term) {
> if (field == term.field() && term.text().startsWith(prefix)) {
> final String target = term.text().substring(prefix.length());
> this.similarity = similarity(target);
> return (similarity > minimumSimilarity);
> }
> endEnum = true;
> return false;
> }
>
> public final float difference() {
> return (float)((similarity  minimumSimilarity) * scale_factor);
> }
>
> public final boolean endEnum() {
> return endEnum;
> }
>
> /******************************
> * Compute Levenshtein distance
> ******************************/
>
> /**
> * Finds and returns the smallest of three integers
> */
> private static final int min(int a, int b, int c) {
> // removed assignments to use double ternary
> return (a < b)
> ? ((a < c) ? a : c)
> : ((b < c) ? b: c);
> // alt form is:
> // if (a < b) { if (a < c) return a; else return c; }
> // if (b < c) return b; else return c;
> }
> /**
> * <p>Similarity returns a number that is 1.0f or less (including negative numbers)
> * based on how similar the Term is compared to a target term. It returns
> * exactly 0.0f when
> * <pre>
> * editDistance < maximumEditDistance</pre>
> * Otherwise it returns:
> * <pre>
> * 1  (editDistance / length)</pre>
> * where length is the length of the shortest term (text or target) including a
> * prefix that are identical and editDistance is the Levenshtein distance for
> * the two words.</p>
> *
> * <p>Embedded within this algorithm is a failfast Levenshtein distance
> * algorithm. The failfast algorithm differs from the standard Levenshtein
> * distance algorithm in that it is aborted if it is discovered that the
> * mimimum distance between the words is greater than some threshold.
> *
> * <p>To calculate the maximum distance threshold we use the following formula:
> * <pre>
> * (1  minimumSimilarity) * length</pre>
> * where length is the shortest term including any prefix that is not part of the
> * similarity comparision. This formula was derived by solving for what maximum value
> * of distance returns false for the following statements:
> * <pre>
> * similarity = 1  ((float)distance / (float) (prefixLength + Math.min(textlen,
targetlen)));
> * return (similarity > minimumSimilarity);</pre>
> * where distance is the Levenshtein distance for the two words.
> * </p>
> * <p>Levenshtein distance (also known as edit distance) is a measure of similiarity
> * between two strings where the distance is measured as the number of character
> * deletions, insertions or substitutions required to transform one string to
> * the other string.
> * @param target the target word or phrase
> * @return the similarity, 0.0 or less indicates that it matches less than the required
> * threshold and 1.0 indicates that the text and target are identical
> */
> private synchronized final float similarity(final String target) {
> final int m = target.length();
> final int n = text.length();
> if (n == 0) {
> //we don't have anything to compare. That means if we just add
> //the letters for m we get the new word
> return prefix.length() == 0 ? 0.0f : 1.0f  ((float) m / prefix.length());
> }
> if (m == 0) {
> return prefix.length() == 0 ? 0.0f : 1.0f  ((float) n / prefix.length());
> }
> final int maxDistance = calculateMaxDistance(m);
> if (maxDistance < Math.abs(mn)) {
> //just adding the characters of m to n or viceversa results in
> //too many edits
> //for example "pre" length is 3 and "prefixes" length is 8. We can see that
> //given this optimal circumstance, the edit distance cannot be less than 5.
> //which is 83 or more precisesly Math.abs(38).
> //if our maximum edit distance is 4, then we can discard this word
> //without looking at it.
> return 0.0f;
> }
> int[] dLast = d0; // set locals for efficiency
> int[] dCurrent = d1;
> for (int j = 0; j <= n; j++) dCurrent[j] = j;
> for (int i = 0; i < m; ) {
> final char s_i = target.charAt(i);
> int[] dTemp = dLast;
> dLast = dCurrent; // previously: d[ii]
> dCurrent = dTemp; // previously: d[i]
> boolean prune = (dCurrent[0] = ++i) > maxDistance; // true if d[i][0] is too
large
> for (int j = 0; j < n; j++) {
> dCurrent[j+1] = (s_i == text.charAt(j))
> ? min(dLast[j+1]+1, dCurrent[j]+1, dLast[j])
> : min(dLast[j+1], dCurrent[j], dLast[j])+1;
> if (prune && dCurrent[j+1] <= maxDistance)
> prune = false;
> }
> // (prune==false) iff (dCurrent[j] < maxDistance) for some j
> if (prune) {
> return 0.0f;
> }
> }
>
> // this will return less than 0.0 when the edit distance is
> // greater than the number of characters in the shorter word.
> // but this was the formula that was previously used in FuzzyTermEnum,
> // so it has not been changed (even though minimumSimilarity must be
> // greater than 0.0)
> return 1.0F  dCurrent[n]/(float)(prefix.length() + Math.min(n,m));
> }
> private int calculateMaxDistance(int m) {
> return (int) ((1minimumSimilarity) * (Math.min(text.length(), m) + prefix.length()));
> }
> /* This is redundant
> public void close() throws IOException {
> super.close(); //call super.close() and let the garbage collector do its work.
> }
> */
>
> }
> package org.apache.lucene.search;
> /**
> * Copyright 2004 The Apache Software Foundation
> *
> * 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/LICENSE2.0
> *
> * 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.
> */
> import org.apache.lucene.index.IndexReader;
> import org.apache.lucene.index.Term;
> import java.io.IOException;
> /** Subclass of FilteredTermEnum for enumerating all terms that are similiar
> * to the specified filter term.
> *
> * <p>Term enumerations are always ordered by Term.compareTo(). Each term in
> * the enumeration is greater than all that precede it.
> */
> public final class FuzzyTermEnum extends FilteredTermEnum {
> /* This should be somewhere around the average long word.
> * If it is longer, we waste time and space. If it is shorter, we waste a
> * little bit of time growing the array as we encounter longer words.
> */
> private static final int TYPICAL_LONGEST_WORD_IN_INDEX = 19;
> /* Allows us save time required to create a new array
> * everytime similarity is called. These are slices that
> * will be reused during dynamic programming handoverhand
> * style. They get resized, if necessary, by growDistanceArrays(int).
> */
> private int[] d0;
> private int[] d1;
> private float similarity;
> private boolean endEnum = false;
> private Term searchTerm = null;
> private final String field;
> private final String text;
> private final String prefix;
> private final float minimumSimilarity;
> private final float scale_factor;
> /**
> * Creates a FuzzyTermEnum with an empty prefix and a minSimilarity of 0.5f.
> * <p>
> * After calling the constructor the enumeration is already pointing to the first
> * valid term if such a term exists.
> *
> * @param reader
> * @param term
> * @throws IOException
> * @see #FuzzyTermEnum(IndexReader, Term, float, int)
> */
> public FuzzyTermEnum(IndexReader reader, Term term) throws IOException {
> this(reader, term, FuzzyQuery.defaultMinSimilarity, FuzzyQuery.defaultPrefixLength);
> }
>
> /**
> * Creates a FuzzyTermEnum with an empty prefix.
> * <p>
> * After calling the constructor the enumeration is already pointing to the first
> * valid term if such a term exists.
> *
> * @param reader
> * @param term
> * @param minSimilarity
> * @throws IOException
> * @see #FuzzyTermEnum(IndexReader, Term, float, int)
> */
> public FuzzyTermEnum(IndexReader reader, Term term, float minSimilarity) throws IOException
{
> this(reader, term, minSimilarity, FuzzyQuery.defaultPrefixLength);
> }
>
> /**
> * Constructor for enumeration of all terms from specified <code>reader</code>
which share a prefix of
> * length <code>prefixLength</code> with <code>term</code>
and which have a fuzzy similarity >
> * <code>minSimilarity</code>.
> * <p>
> * After calling the constructor the enumeration is already pointing to the first
> * valid term if such a term exists.
> *
> * @param reader Delivers terms.
> * @param term Pattern term.
> * @param minSimilarity Minimum required similarity for terms from the reader. Default
value is 0.5f.
> * @param prefixLength Length of required common prefix. Default value is 0.
> * @throws IOException
> */
> public FuzzyTermEnum(IndexReader reader, Term term, final float minSimilarity, final
int prefixLength) throws IOException {
> super();
>
> if (minSimilarity >= 1.0f)
> throw new IllegalArgumentException("minimumSimilarity cannot be greater than or
equal to 1");
> else if (minSimilarity < 0.0f)
> throw new IllegalArgumentException("minimumSimilarity cannot be less than 0");
> if(prefixLength < 0)
> throw new IllegalArgumentException("prefixLength cannot be less than 0");
> this.minimumSimilarity = minSimilarity;
> this.scale_factor = 1.0f / (1.0f  minimumSimilarity);
> this.searchTerm = term;
> this.field = searchTerm.field();
> //The prefix could be longer than the word.
> //It's kind of silly though. It means we must match the entire word.
> final int fullSearchTermLength = searchTerm.text().length();
> final int realPrefixLength = prefixLength > fullSearchTermLength ? fullSearchTermLength
: prefixLength;
> this.text = searchTerm.text().substring(realPrefixLength);
> this.prefix = searchTerm.text().substring(0, realPrefixLength);
> growDistanceArrays(TYPICAL_LONGEST_WORD_IN_INDEX);
> setEnum(reader.terms(new Term(searchTerm.field(), prefix)));
> }
> /**
> * The termCompare method in FuzzyTermEnum uses Levenshtein distance to
> * calculate the distance between the given term and the comparing term.
> */
> protected final boolean termCompare(Term term) {
> if (field == term.field() && term.text().startsWith(prefix)) {
> final String target = term.text().substring(prefix.length());
> this.similarity = similarity(target);
> return (similarity > minimumSimilarity);
> }
> endEnum = true;
> return false;
> }
>
> public final float difference() {
> return (float)((similarity  minimumSimilarity) * scale_factor);
> }
>
> public final boolean endEnum() {
> return endEnum;
> }
>
> /******************************
> * Compute Levenshtein distance
> ******************************/
>
> /**
> * Finds and returns the smallest of three integers
> */
> private static final int min(int a, int b, int c) {
> // removed assignments to use double ternary
> return (a < b)
> ? ((a < c) ? a : c)
> : ((b < c) ? b: c);
> // alt form is:
> // if (a < b) { if (a < c) return a; else return c; }
> // if (b < c) return b; else return c;
> }
> /**
> * <p>Similarity returns a number that is 1.0f or less (including negative numbers)
> * based on how similar the Term is compared to a target term. It returns
> * exactly 0.0f when
> * <pre>
> * editDistance < maximumEditDistance</pre>
> * Otherwise it returns:
> * <pre>
> * 1  (editDistance / length)</pre>
> * where length is the length of the shortest term (text or target) including a
> * prefix that are identical and editDistance is the Levenshtein distance for
> * the two words.</p>
> *
> * <p>Embedded within this algorithm is a failfast Levenshtein distance
> * algorithm. The failfast algorithm differs from the standard Levenshtein
> * distance algorithm in that it is aborted if it is discovered that the
> * mimimum distance between the words is greater than some threshold.
> *
> * <p>To calculate the maximum distance threshold we use the following formula:
> * <pre>
> * (1  minimumSimilarity) * length</pre>
> * where length is the shortest term including any prefix that is not part of the
> * similarity comparision. This formula was derived by solving for what maximum value
> * of distance returns false for the following statements:
> * <pre>
> * similarity = 1  ((float)distance / (float) (prefixLength + Math.min(textlen,
targetlen)));
> * return (similarity > minimumSimilarity);</pre>
> * where distance is the Levenshtein distance for the two words.
> * </p>
> * <p>Levenshtein distance (also known as edit distance) is a measure of similiarity
> * between two strings where the distance is measured as the number of character
> * deletions, insertions or substitutions required to transform one string to
> * the other string.
> * @param target the target word or phrase
> * @return the similarity, 0.0 or less indicates that it matches less than the required
> * threshold and 1.0 indicates that the text and target are identical
> */
> private synchronized final float similarity(final String target) {
> final int m = target.length();
> final int n = text.length();
> if (n == 0) {
> //we don't have anything to compare. That means if we just add
> //the letters for m we get the new word
> return prefix.length() == 0 ? 0.0f : 1.0f  ((float) m / prefix.length());
> }
> if (m == 0) {
> return prefix.length() == 0 ? 0.0f : 1.0f  ((float) n / prefix.length());
> }
> final int maxDistance = calculateMaxDistance(m);
> if (maxDistance < Math.abs(mn)) {
> //just adding the characters of m to n or viceversa results in
> //too many edits
> //for example "pre" length is 3 and "prefixes" length is 8. We can see that
> //given this optimal circumstance, the edit distance cannot be less than 5.
> //which is 83 or more precisesly Math.abs(38).
> //if our maximum edit distance is 4, then we can discard this word
> //without looking at it.
> return 0.0f;
> }
> //let's make sure we have enough room in our array to do the distance calculations.
> if (d0.length <= m) {
> growDistanceArrays(m);
> }
> int[] dLast = d0; // set local vars for efficiency ~ the old d[i1]
> int[] dCurrent = d1; // ~ the old d[i]
> for (int j = 0; j <= m; j++) dCurrent[j] = j;
> for (int i = 0; i < n; ) {
> final char s_i = text.charAt(i);
> int[] dTemp = dLast;
> dLast = dCurrent; // previously: d[ii]
> dCurrent = dTemp; // previously: d[i]
> boolean prune = (dCurrent[0] = ++i) > maxDistance; // true if d[i][0] is too large
> for (int j = 0; j < m; j++) {
> dCurrent[j+1] = (s_i == target.charAt(j))
> ? min(dLast[j+1]+1, dCurrent[j]+1, dLast[j])
> : min(dLast[j+1], dCurrent[j], dLast[j])+1;
> if (prune && dCurrent[j+1] <= maxDistance)
> prune = false;
> }
> // (prune==false) iff (dCurrent[j] < maxDistance) for some j
> if (prune) {
> return 0.0f;
> }
> }
> // this will return less than 0.0 when the edit distance is
> // greater than the number of characters in the shorter word.
> // but this was the formula that was previously used in FuzzyTermEnum,
> // so it has not been changed (even though minimumSimilarity must be
> // greater than 0.0)
> return 1.0F  dCurrent[m]/(float)(prefix.length() + Math.min(n,m));
> }
> /**
> * Grow the second dimension of the array slices, so that we can
> * calculate the Levenshtein difference.
> */
> private void growDistanceArrays(int m) {
> d0 = new int[m+1];
> d1 = new int[m+1];
> }
> private int calculateMaxDistance(int m) {
> return (int) ((1minimumSimilarity) * (Math.min(text.length(), m) + prefix.length()));
> }
> /* This is redundant
> public void close() throws IOException {
> super.close(); //call super.close() and let the garbage collector do its work.
> }
> */
>
> }

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