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275 lines
9.3 KiB
JavaScript
275 lines
9.3 KiB
JavaScript
/*
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didYouMean.js - A simple JavaScript matching engine
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===================================================
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[Available on GitHub](https://github.com/dcporter/didyoumean.js).
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A super-simple, highly optimized JS library for matching human-quality input to a list of potential
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matches. You can use it to suggest a misspelled command-line utility option to a user, or to offer
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links to nearby valid URLs on your 404 page. (The examples below are taken from a personal project,
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my [HTML5 business card](http://dcporter.aws.af.cm/me), which uses didYouMean.js to suggest correct
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URLs from misspelled ones, such as [dcporter.aws.af.cm/me/instagarm](http://dcporter.aws.af.cm/me/instagarm).)
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Uses the [Levenshtein distance algorithm](https://en.wikipedia.org/wiki/Levenshtein_distance).
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didYouMean.js works in the browser as well as in node.js. To install it for use in node:
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```
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npm install didyoumean
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```
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Examples
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--------
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Matching against a list of strings:
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```
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var input = 'insargrm'
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var list = ['facebook', 'twitter', 'instagram', 'linkedin'];
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console.log(didYouMean(input, list));
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> 'instagram'
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// The method matches 'insargrm' to 'instagram'.
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input = 'google plus';
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console.log(didYouMean(input, list));
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> null
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// The method was unable to find 'google plus' in the list of options.
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```
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Matching against a list of objects:
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```
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var input = 'insargrm';
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var list = [ { id: 'facebook' }, { id: 'twitter' }, { id: 'instagram' }, { id: 'linkedin' } ];
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var key = 'id';
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console.log(didYouMean(input, list, key));
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> 'instagram'
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// The method returns the matching value.
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didYouMean.returnWinningObject = true;
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console.log(didYouMean(input, list, key));
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> { id: 'instagram' }
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// The method returns the matching object.
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```
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didYouMean(str, list, [key])
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----------------------------
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- str: The string input to match.
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- list: An array of strings or objects to match against.
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- key (OPTIONAL): If your list array contains objects, you must specify the key which contains the string
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to match against.
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Returns: the closest matching string, or null if no strings exceed the threshold.
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Options
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-------
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Options are set on the didYouMean function object. You may change them at any time.
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### threshold
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By default, the method will only return strings whose edit distance is less than 40% (0.4x) of their length.
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For example, if a ten-letter string is five edits away from its nearest match, the method will return null.
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You can control this by setting the "threshold" value on the didYouMean function. For example, to set the
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edit distance threshold to 50% of the input string's length:
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```
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didYouMean.threshold = 0.5;
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```
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To return the nearest match no matter the threshold, set this value to null.
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### thresholdAbsolute
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This option behaves the same as threshold, but instead takes an integer number of edit steps. For example,
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if thresholdAbsolute is set to 20 (the default), then the method will only return strings whose edit distance
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is less than 20. Both options apply.
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### caseSensitive
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By default, the method will perform case-insensitive comparisons. If you wish to force case sensitivity, set
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the "caseSensitive" value to true:
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```
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didYouMean.caseSensitive = true;
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```
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### nullResultValue
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By default, the method will return null if there is no sufficiently close match. You can change this value here.
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### returnWinningObject
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By default, the method will return the winning string value (if any). If your list contains objects rather
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than strings, you may set returnWinningObject to true.
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```
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didYouMean.returnWinningObject = true;
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```
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This option has no effect on lists of strings.
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### returnFirstMatch
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By default, the method will search all values and return the closest match. If you're simply looking for a "good-
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enough" match, you can set your thresholds appropriately and set returnFirstMatch to true to substantially speed
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things up.
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License
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-------
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didYouMean copyright (c) 2013-2014 Dave Porter.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License
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[here](http://www.apache.org/licenses/LICENSE-2.0).
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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(function() {
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"use strict";
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// The didYouMean method.
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function didYouMean(str, list, key) {
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if (!str) return null;
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// If we're running a case-insensitive search, smallify str.
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if (!didYouMean.caseSensitive) { str = str.toLowerCase(); }
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// Calculate the initial value (the threshold) if present.
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var thresholdRelative = didYouMean.threshold === null ? null : didYouMean.threshold * str.length,
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thresholdAbsolute = didYouMean.thresholdAbsolute,
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winningVal;
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if (thresholdRelative !== null && thresholdAbsolute !== null) winningVal = Math.min(thresholdRelative, thresholdAbsolute);
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else if (thresholdRelative !== null) winningVal = thresholdRelative;
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else if (thresholdAbsolute !== null) winningVal = thresholdAbsolute;
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else winningVal = null;
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// Get the edit distance to each option. If the closest one is less than 40% (by default) of str's length,
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// then return it.
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var winner, candidate, testCandidate, val,
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i, len = list.length;
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for (i = 0; i < len; i++) {
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// Get item.
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candidate = list[i];
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// If there's a key, get the candidate value out of the object.
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if (key) { candidate = candidate[key]; }
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// Gatekeep.
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if (!candidate) { continue; }
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// If we're running a case-insensitive search, smallify the candidate.
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if (!didYouMean.caseSensitive) { testCandidate = candidate.toLowerCase(); }
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else { testCandidate = candidate; }
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// Get and compare edit distance.
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val = getEditDistance(str, testCandidate, winningVal);
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// If this value is smaller than our current winning value, OR if we have no winning val yet (i.e. the
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// threshold option is set to null, meaning the caller wants a match back no matter how bad it is), then
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// this is our new winner.
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if (winningVal === null || val < winningVal) {
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winningVal = val;
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// Set the winner to either the value or its object, depending on the returnWinningObject option.
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if (key && didYouMean.returnWinningObject) winner = list[i];
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else winner = candidate;
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// If we're returning the first match, return it now.
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if (didYouMean.returnFirstMatch) return winner;
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}
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}
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// If we have a winner, return it.
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return winner || didYouMean.nullResultValue;
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}
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// Set default options.
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didYouMean.threshold = 0.4;
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didYouMean.thresholdAbsolute = 20;
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didYouMean.caseSensitive = false;
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didYouMean.nullResultValue = null;
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didYouMean.returnWinningObject = null;
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didYouMean.returnFirstMatch = false;
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// Expose.
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// In node...
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if (typeof module !== 'undefined' && module.exports) {
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module.exports = didYouMean;
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}
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// Otherwise...
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else {
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window.didYouMean = didYouMean;
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}
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var MAX_INT = Math.pow(2,32) - 1; // We could probably go higher than this, but for practical reasons let's not.
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function getEditDistance(a, b, max) {
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// Handle null or undefined max.
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max = max || max === 0 ? max : MAX_INT;
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var lena = a.length;
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var lenb = b.length;
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// Fast path - no A or B.
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if (lena === 0) return Math.min(max + 1, lenb);
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if (lenb === 0) return Math.min(max + 1, lena);
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// Fast path - length diff larger than max.
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if (Math.abs(lena - lenb) > max) return max + 1;
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// Slow path.
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var matrix = [],
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i, j, colMin, minJ, maxJ;
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// Set up the first row ([0, 1, 2, 3, etc]).
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for (i = 0; i <= lenb; i++) { matrix[i] = [i]; }
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// Set up the first column (same).
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for (j = 0; j <= lena; j++) { matrix[0][j] = j; }
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// Loop over the rest of the columns.
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for (i = 1; i <= lenb; i++) {
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colMin = MAX_INT;
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minJ = 1;
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if (i > max) minJ = i - max;
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maxJ = lenb + 1;
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if (maxJ > max + i) maxJ = max + i;
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// Loop over the rest of the rows.
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for (j = 1; j <= lena; j++) {
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// If j is out of bounds, just put a large value in the slot.
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if (j < minJ || j > maxJ) {
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matrix[i][j] = max + 1;
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}
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// Otherwise do the normal Levenshtein thing.
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else {
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// If the characters are the same, there's no change in edit distance.
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if (b.charAt(i - 1) === a.charAt(j - 1)) {
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matrix[i][j] = matrix[i - 1][j - 1];
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}
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// Otherwise, see if we're substituting, inserting or deleting.
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else {
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matrix[i][j] = Math.min(matrix[i - 1][j - 1] + 1, // Substitute
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Math.min(matrix[i][j - 1] + 1, // Insert
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matrix[i - 1][j] + 1)); // Delete
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}
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}
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// Either way, update colMin.
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if (matrix[i][j] < colMin) colMin = matrix[i][j];
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}
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// If this column's minimum is greater than the allowed maximum, there's no point
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// in going on with life.
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if (colMin > max) return max + 1;
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}
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// If we made it this far without running into the max, then return the final matrix value.
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return matrix[lenb][lena];
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}
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})();
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