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?

Answer 1

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

Answer 2

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);

Answer 3

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"

Answer 4

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();

        }
    }