javascript 用Javascript检测两个字符串之间的差异

detect differences between two strings with Javascript

提问by Wesley Smith

With Javascript, I want to check how many differences there are between two strings.

使用 Javascript，我想检查两个字符串之间有多少差异。

Something like:

就像是：

var oldName = "Alec";
var newName = "Alexander";
var differences = getDifference(oldName, newName) // differences = 6

• Any letters added to the name should count as one change per letter.
• Changing a letter should count as a change per letter. Swaping two
• letters should count as two changes as your really changing each
  leter.
• However, shifting a letter and inserting another should only count as one change.

• 添加到名称中的任何字母都应计为每个字母的一次更改。
• 更改一个字母应该算作每个字母的更改。交换两个
• 字母应该算作两次更改，因为您真正更改了每个
  字母。
• 但是，移动一个字母并插入另一个字母只能算作一次更改。

For example:

例如：

Changing "Alex" to "Alexander" would be 5 changes as 5 letters have been added

将“亚历克斯”更改为“亚历山大”将是 5 次更改，因为已添加 5 个字母

Changing "Alex" to "Allex" would only be one change as you added an "l" and shifted the rest over but didnt change them

将“亚历克斯”更改为“亚历克斯”只会是一个更改，因为您添加了“l”并将其余部分移过来但没有更改它们

Changing "Alexander" to "Allesander"would be 2 changes (adding the "l" and changing "x" to a "s").

将“Alexander”更改为“Allesander”将是 2 个更改（添加“l”并将“x”更改为“s”）。

I can split each name into an array of letters and compare them easy enough like in this jsFiddlewith the below function:

我可以将每个名称拆分为一个字母数组，并像在此jsFiddle 中一样轻松地将它们与以下函数进行比较：

function compareNames(){
    var oldName = $('#old').val().split("");
    var newName = $('#new').val().split("");
    var changeCount = 0;
    var testLength = 0;
    if(oldName.length > newName.length){
        testLength=oldName.length;    
    }
    else testLength=newName.length;
    for(var i=0;i<testLength;i++){
        if(oldName[i]!=newName[i]) {
           changeCount++;           
        }
    }
    alert(changeCount);
}

But how can I account for the shifting of letters not counting as a change?

但是我怎么能解释信件的变化不算是变化呢？

---

---

Update: Here's how I got it working

更新：这是我的工作方式

Levenshtein distancewas exactly what I needed. Thanks to Peter!

Levenshtein 距离正是我所需要的。感谢彼得！

Working jsFiddle

工作 jsFiddle

$(function () {
    $('#compare').click(function () {
        var oldName = $('.compare:eq(0)').val();
        var newName = $('.compare:eq(1)').val();
        var count = levDist(oldName, newName);
        $('#display').html('There are ' + count + ' differences present');
    });
});

function levDist(s, t) {
    var d = []; //2d matrix

    // Step 1
    var n = s.length;
    var m = t.length;

    if (n == 0) return m;
    if (m == 0) return n;

    //Create an array of arrays in javascript (a descending loop is quicker)
    for (var i = n; i >= 0; i--) d[i] = [];

    // Step 2
    for (var i = n; i >= 0; i--) d[i][0] = i;
    for (var j = m; j >= 0; j--) d[0][j] = j;

    // Step 3
    for (var i = 1; i <= n; i++) {
        var s_i = s.charAt(i - 1);

        // Step 4
        for (var j = 1; j <= m; j++) {

            //Check the jagged ld total so far
            if (i == j && d[i][j] > 4) return n;

            var t_j = t.charAt(j - 1);
            var cost = (s_i == t_j) ? 0 : 1; // Step 5

            //Calculate the minimum
            var mi = d[i - 1][j] + 1;
            var b = d[i][j - 1] + 1;
            var c = d[i - 1][j - 1] + cost;

            if (b < mi) mi = b;
            if (c < mi) mi = c;

            d[i][j] = mi; // Step 6

            //Damerau transposition
            if (i > 1 && j > 1 && s_i == t.charAt(j - 2) && s.charAt(i - 2) == t_j) {
                d[i][j] = Math.min(d[i][j], d[i - 2][j - 2] + cost);
            }
        }
    }
    // Step 7
    return d[n][m];
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js"></script>
<input type="button" id="compare" value="Compare" /><br><br>
<input type="text" id="old" class="compare" value="Alec" />
<input type="text" id="new" class="compare" value="Alexander" />
<br>
<br>
<span id="display"></span>

Credit to James Westgate for the function:

归功于 James Westgate 的功能：

Jame's post showing this function

James 的帖子展示了这个功能

采纳答案by Peter

I don't have a Javascript implementation on hand per se, but you're doing something for which well-established algorithms exist. Specifically, I believe you're looking for the "Levenshtein distance" between two strings -- i.e. the number of insertions, substitutions and deletions (assuming you are treating a deletion as a change).

我手头没有 Javascript 实现本身，但您正在做一些存在完善算法的事情。具体来说，我相信您正在寻找两个字符串之间的“Levenshtein 距离”——即插入、替换和删除的数量（假设您将删除视为更改）。

The wikipedia page for Levenshtein distancehas various pseudo-code implementations from which you could start, and references which may also help you.

Levenshtein distance 的维基百科页面有各种伪代码实现，您可以从中开始，参考也可能对您有所帮助。

回答by ClojureMostly

Alternative implemenation:

替代实现：

/**
 * Computes the Levenshtein edit distance between two strings.
 * @param {string} a
 * @param {string} b
 * @return {number} The edit distance between the two strings.
 */
goog.string.editDistance = function(a, b) {
  var v0 = [];
  var v1 = [];

  if (a == b) {
    return 0;
  }

  if (!a.length || !b.length) {
    return Math.max(a.length, b.length);
  }

  for (var i = 0; i < b.length + 1; i++) {
    v0[i] = i;
  }

  for (var i = 0; i < a.length; i++) {
    v1[0] = i + 1;

    for (var j = 0; j < b.length; j++) {
      var cost = Number(a[i] != b[j]);
      // Cost for the substring is the minimum of adding one character, removing
      // one character, or a swap.
      v1[j + 1] = Math.min(v1[j] + 1, v0[j + 1] + 1, v0[j] + cost);
    }

    for (var j = 0; j < v0.length; j++) {
      v0[j] = v1[j];
    }
  }

  return v1[b.length];
};