How can I calculate similarity between two strings in C#?

Question

I'm looking to assess similarity (including case) between two strings and give a value between 0 and 1.

I tried the Levenshtein distance implementation but it only gives integers and does not compare inner alphabets.

For eg comparing "ABCD" and "Abcd" gives distance of 3 and "AOOO" also gives a distance of 3 but clearly "Abcd" is better match than "AOOO".

So compared to "ABCD" I want "ABcd" to be most similar then "Abcd" then "AOOO" then "AOOOO"

I've also looked here but I am not looking for a variable length algorithm.

Thanks

Answer 1

Try something like this

double d = (LevenshteinDist(s, t) + LevenshteinDist(s.ToLower(), t.ToLower())) /
           2.0 * Math.Max(s.Length, t.Length);

If you want to give less importance to case differences than letter differences, you can give different weights to the terms

double d = (0.15*LevenshteinDist(s, t) + 
            0.35*LevenshteinDist(s.ToLower(), t.ToLower())) /
           Math.Max(s.Length, t.Length);

Note that the weights sum up to 0.5, thus makting the division by 2.0 obsolete.

Answer 2

    bool check(string[] a, string s)
    {
        for (int i = 0; i < a.Length; i++)
            if (s == a[i])
                return true;
        return false;
    }

    public double simi(string string1, string string2)
    {
        int sub1 = 0;
        int sub2 = 0;
        string[] sp1 = new string[string1.Length - 1];
        string[] sp2 = new string[string2.Length - 1];
        string[] sp3 = new string[string1.Length - 1];
        string[] sp4 = new string[string2.Length - 1];
        for (int i = 0; i < string1.Length - 1; i++)
        {
            string x = "";
            x = string1.Substring(i, 2);

            sp1[sub1] = x;
            ++sub1;
        }
        for (int i = 0; i < string2.Length - 1; i++)
        {
            string x = "";
            x = string2.Substring(i, 2);
            sp2[sub2] = x;
            ++sub2;
        }


        int j = 0, k = 0;

        for (int i = 0; i < sp1.Length; i++)
            if (check(sp3, sp1[i]) == true)
            {

                continue;
            }
            else
            {
                sp3[j] = sp1[i];
                j++;

            }

        for (int i = 0; i < sp2.Length; i++)
            if (check(sp4, sp2[i]) == true)
            {

                continue;
            }
            else
            {
                sp4[k] = sp2[i];
                k++;


            }

        Array.Resize(ref sp3, j);
        Array.Resize(ref sp4, k);

        Array.Sort<string>(sp3);
        Array.Sort<string>(sp4);

        int n = 0;


        for (int i = 0; i < sp3.Length; i++)
        {

            if (check(sp4, sp3[i]))
            {

                n++;
            }


        }

        double resulte;

        int l1 = sp3.Length;
        int l2 = sp4.Length;

        resulte = ((2.0 * Convert.ToDouble(n)) / Convert.ToDouble(l1 + l2)) * 100;

        return resulte;
    }

Answer 3

Adapt Levenshtein Distance with a custom table T. Let the cost of insertion = 1. The cost of deletion also 1. Let T(c,d) denote the penalty of replacing c with d. T(c,c) should be = 0. T(c,d) should be <= 2.

Define Max(n,m) be the maximum theoretical distance of strings of length n and m. Obviously, Max(n,m) = n+m.

Define Distance(s,t) be the cost of changing s to t divided by Max(s,t). There you go.

Be careful in defining T so that the definition obeys distance axioms:

• Distance(s,s) = 0
• Distance(s,t) = Distance(t,s)
• Distance(s,t) <= Distance(s,u) + Distance(u,t)

Then it will be more useful in more situations.