Compare Strings Javascript Return %of Likely

Question

I am looking for a JavaScript function that can compare two strings and return the likeliness that they are alike. I have looked at soundex but that's not really great for multi-word strings or non-names. I am looking for a function like:

    function compare(strA,strB){          }          compare("Apples","apple") = Some X Percentage. 

The function would work with all types of strings, including numbers, multi-word values, and names. Perhaps there's a simple algorithm I could use?

Ultimately none of these served my purpose so I used this:

     function compare(c, u) {             var incept = false;             var ca = c.split(",");             u = clean(u);             //ca = correct answer array (Collection of all correct answer)             //caa = a single correct answer word array (collection of words of a single correct answer)             //u = array of user answer words cleaned using custom clean function             for (var z = 0; z < ca.length; z++) {                 caa = $.trim(ca[z]).split(" ");                 var pc = 0;                 for (var x = 0; x < caa.length; x++) {                     for (var y = 0; y < u.length; y++) {                         if (soundex(u[y]) != null && soundex(caa[x]) != null) {                             if (soundex(u[y]) == soundex(caa[x])) {                                 pc = pc + 1;                             }                         }                         else {                             if (u[y].indexOf(caa[x]) > -1) {                                 pc = pc + 1;                             }                         }                     }                 }                 if ((pc / caa.length) > 0.5) {                     return true;                 }             }             return false;         }                  // create object listing the SOUNDEX values for each letter         // -1 indicates that the letter is not coded, but is used for coding         //  0 indicates that the letter is omitted for modern census archives         //                              but acts like -1 for older census archives         //  1 is for BFPV         //  2 is for CGJKQSXZ         //  3 is for DT         //  4 is for L         //  5 is for MN my home state         //  6 is for R         function makesoundex() {             this.a = -1             this.b = 1             this.c = 2             this.d = 3             this.e = -1             this.f = 1             this.g = 2             this.h = 0             this.i = -1             this.j = 2             this.k = 2             this.l = 4             this.m = 5             this.n = 5             this.o = -1             this.p = 1             this.q = 2             this.r = 6             this.s = 2             this.t = 3             this.u = -1             this.v = 1             this.w = 0             this.x = 2             this.y = -1             this.z = 2         }                  var sndx = new makesoundex()                  // check to see that the input is valid         function isSurname(name) {             if (name == "" || name == null) {                 return false             } else {                 for (var i = 0; i < name.length; i++) {                     var letter = name.charAt(i)                     if (!(letter >= 'a' && letter <= 'z' || letter >= 'A' && letter <= 'Z')) {                         return false                     }                 }             }             return true         }                  // Collapse out directly adjacent sounds         // 1. Assume that surname.length>=1         // 2. Assume that surname contains only lowercase letters         function collapse(surname) {             if (surname.length == 1) {                 return surname             }             var right = collapse(surname.substring(1, surname.length))             if (sndx[surname.charAt(0)] == sndx[right.charAt(0)]) {                 return surname.charAt(0) + right.substring(1, right.length)             }             return surname.charAt(0) + right         }                  // Collapse out directly adjacent sounds using the new National Archives method         // 1. Assume that surname.length>=1         // 2. Assume that surname contains only lowercase letters         // 3. H and W are completely ignored         function omit(surname) {             if (surname.length == 1) {                 return surname             }             var right = omit(surname.substring(1, surname.length))             if (!sndx[right.charAt(0)]) {                 return surname.charAt(0) + right.substring(1, right.length)             }             return surname.charAt(0) + right         }                  // Output the coded sequence         function output_sequence(seq) {             var output = seq.charAt(0).toUpperCase() // Retain first letter             output += "-" // Separate letter with a dash             var stage2 = seq.substring(1, seq.length)             var count = 0             for (var i = 0; i < stage2.length && count < 3; i++) {                 if (sndx[stage2.charAt(i)] > 0) {                     output += sndx[stage2.charAt(i)]                     count++                 }             }             for (; count < 3; count++) {                 output += "0"             }             return output         }                  // Compute the SOUNDEX code for the surname         function soundex(value) {             if (!isSurname(value)) {                 return null             }             var stage1 = collapse(value.toLowerCase())             //form.result.value=output_sequence(stage1);                      var stage1 = omit(value.toLowerCase())             var stage2 = collapse(stage1)             return output_sequence(stage2);                  }                  function clean(u) {             var u = u.replace(/\,/g, "");             u = u.toLowerCase().split(" ");             var cw = ["ARRAY OF WORDS TO BE EXCLUDED FROM COMPARISON"];             var n = [];             for (var y = 0; y < u.length; y++) {                 var test = false;                 for (var z = 0; z < cw.length; z++) {                     if (u[y] != "" && u[y] != cw[z]) {                         test = true;                         break;                     }                 }                 if (test) {         //Don't use & or $ in comparison                     var val = u[y].replace("$", "").replace("&", "");                     n.push(val);                 }             }             return n;         } 

Answer 1

Here's an answer based on Levenshtein distance https://en.wikipedia.org/wiki/Levenshtein_distance

function similarity(s1, s2) {   var longer = s1;   var shorter = s2;   if (s1.length < s2.length) {     longer = s2;     shorter = s1;   }   var longerLength = longer.length;   if (longerLength == 0) {     return 1.0;   }   return (longerLength - editDistance(longer, shorter)) / parseFloat(longerLength); } 

For calculating edit distance

function editDistance(s1, s2) {   s1 = s1.toLowerCase();   s2 = s2.toLowerCase();    var costs = new Array();   for (var i = 0; i <= s1.length; i++) {     var lastValue = i;     for (var j = 0; j <= s2.length; j++) {       if (i == 0)         costs[j] = j;       else {         if (j > 0) {           var newValue = costs[j - 1];           if (s1.charAt(i - 1) != s2.charAt(j - 1))             newValue = Math.min(Math.min(newValue, lastValue),               costs[j]) + 1;           costs[j - 1] = lastValue;           lastValue = newValue;         }       }     }     if (i > 0)       costs[s2.length] = lastValue;   }   return costs[s2.length]; } 

Usage

similarity('Stack Overflow','Stack Ovrflw') 

returns 0.8571428571428571

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You can play with it below:

function checkSimilarity(){    var str1 = document.getElementById("lhsInput").value;    var str2 = document.getElementById("rhsInput").value;    document.getElementById("output").innerHTML = similarity(str1, str2);  }    function similarity(s1, s2) {        var longer = s1;        var shorter = s2;        if (s1.length < s2.length) {          longer = s2;          shorter = s1;        }        var longerLength = longer.length;        if (longerLength == 0) {          return 1.0;        }        return (longerLength - editDistance(longer, shorter)) / parseFloat(longerLength);      }        function editDistance(s1, s2) {        s1 = s1.toLowerCase();        s2 = s2.toLowerCase();          var costs = new Array();        for (var i = 0; i <= s1.length; i++) {          var lastValue = i;          for (var j = 0; j <= s2.length; j++) {            if (i == 0)              costs[j] = j;            else {              if (j > 0) {                var newValue = costs[j - 1];                if (s1.charAt(i - 1) != s2.charAt(j - 1))                  newValue = Math.min(Math.min(newValue, lastValue),                    costs[j]) + 1;                costs[j - 1] = lastValue;                lastValue = newValue;              }            }          }          if (i > 0)            costs[s2.length] = lastValue;        }        return costs[s2.length];      }

<div><label for="lhsInput">String 1:</label> <input type="text" id="lhsInput" oninput="checkSimilarity()" /></div>  <div><label for="rhsInput">String 2:</label> <input type="text" id="rhsInput" oninput="checkSimilarity()" /></div>  <div>Match: <span id="output">No Input</span></div>

Answer 2

Using this library for string similarity worked like a charm for me!

Here's the Example -

var similarity = stringSimilarity.compareTwoStrings("Apples","apple");    // => 0.88