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

---

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>