Diff comparison word by word and display changes

Question

Could be marked as duplicated, but I haven't found a propper solution yet.

I need to write a function that compares 2 pieces of text word by word, and prints out the text showing added/deleted/changed words. For example:

StringOriginal = "I am Tim and I am 27 years old"

StringEdited = "I am Kim and I am not that old".

Result: I am Tim Kim and I am 27 years not that old.

Most of the diff algorithms I find tend to compare char by char. this works fine, untill you have a 2 different words on the same index, with mutual chars.

"I am Tim" edited to "I am Kim" Results into:

I am TKim

instead of

I am Tim Kim.

Any pointers?

score 0 · Answer 1 · answered Oct 24 '17 at 12:28

0

Split by space both StringOriginal and StringEdited. Loop thru each word of StringOriginal comparing it to the same word index from Edited. Every unequal word should be put to a temporary variable and concatenate it to the result only when you get equal word again from the loop. Use StringBuilder in creating the result. Hope this helps

answered Oct 24 '17 at 12:28

proxies

246
1
6

Thanks, got me started! – Tim Maes Oct 24 '17 at 12:58

score 0 · Answer 2 · answered Oct 24 '17 at 12:34

Split both strings by space, join the resulting arrays via Union, then back to string like this:

string[] arr1 = str1.Split(' ');
string[] arr2 = str1.Split(' ');

var merged = arr1.Union(arr2).ToArray<string>();

var mergedString = string.Join(' ', merged);

score 0 · Answer 3 · answered Oct 24 '17 at 13:14

little bit old fashion, but you can try this.

    string StringOriginal = "I am Tim and I am 27 years old";
    string StringEdited = "I am Kim and I am not that old";

    string[] StringOriginalArray = StringOriginal.Split();
    string[] StringEditedArray = StringEdited.Split();
    string[] newStringArray = new string[StringOriginalArray.Length + StringEditedArray.Length];

    int i = 0;
    int io = 0;
    int ie = 0;

    while (i < newStringArray.Length)
    {
        if (io < StringOriginalArray.Length)
        {
            newStringArray[i] = StringOriginalArray[io];
            io++;
            i++;
        }
        if (ie < StringEditedArray.Length)
        {
            newStringArray[i] = StringEditedArray[ie];
            ie++;
            i++;
        }
    }

    string[] finalArray = new string[newStringArray.Length];
    int f = 0;
    for (int k = 0; k < newStringArray.Length; k=k+2)
    {
        finalArray[f++] = newStringArray[k];
        if (newStringArray[k] != newStringArray[k+1])
        {
            finalArray[f++] = newStringArray[k+1];
        }
    }

    Console.WriteLine(String.Join(" ", finalArray));

Output:

"I am Tim Kim and I am 27 not years that old"

This works! I just need to edit it to highlight added/deleted words in green/red in my asp.net application! Thanks! — Tim Maes, Oct 24 '17 at 13:20

score 0 · Answer 4 · answered Feb 03 '19 at 15:15

been looking for an answer myself to this question. haven't been able to find a good solution. came up with the following. but it's not perfect.

    public static class DiffEngine
    {
        private static Regex r = new Regex(@"(?<=[\s])", RegexOptions.Compiled);

        public static string Process(ref string TextA, ref string TextB)
        {
            var A = r.Split(TextA);
            var B = r.Split(TextB);
            var max = Math.Max(A.Count(), B.Count());
            var sbDel = new StringBuilder("<del>");
            var sbIns = new StringBuilder("<ins>");
            var sbOutput = new StringBuilder();
            var aCurr = string.Empty;
            var bCurr = string.Empty;
            var aNext = string.Empty;
            var bNext = string.Empty;

            for (int i = 0; i < max; i++)
            {
                aCurr = (i > A.Count() - 1) ? string.Empty : A[i];
                bCurr = (i > B.Count() - 1) ? string.Empty : B[i];
                aNext = (i > A.Count() - 2) ? string.Empty : A[i + 1];
                bNext = (i > B.Count() - 2) ? string.Empty : B[i + 1];

                if (aCurr == bCurr)
                {
                    sbOutput.Append(aCurr);
                }
                else
                {
                    if (aNext != bNext)
                    {
                        sbDel.Append(aCurr);
                        sbIns.Append(bCurr);
                    }
                    else
                    {
                        sbDel.Append(aCurr);
                        sbIns.Append(bCurr);
                        sbOutput
                            .Append(sbDel.ToString())
                            .Append("</del>")
                            .Append(sbIns.ToString())
                            .Append("</ins>");
                        sbDel.Clear().Append("<del>");
                        sbIns.Clear().Append("<ins>");
                    }
                }
            }

            A = null;
            B = null;
            sbDel = null;
            sbIns = null;
            return sbOutput.ToString();

        }
    }

Diff comparison word by word and display changes

4 Answers4