Generate a unique string based on a pair of string

Question

I've two strings StringA, StringB. I want to generate a unique string to denote this pair.

i.e.

f(x, y) should be unique for every x, y and f(x, y) = f(y, x) where x, y are strings.

Any ideas?

Answer 1

I think the following should yield unique strings:

String f = Replace(StringA<StringB?StringA:StringB,"@","@@") + "}@{" + Replace(StringA<StringB?StringB:StringA,"@","@@")

(That is, there's only one place in the string where a single "@" sign can appear, and we don't have to worry about a run of "@"s at the end of StringA being confused with a run of "@"s at the start of StringB.

Answer 2

Just find a unique way of ordering them and concatenate with a separator.

def uniqueStr(strA,strB,sep):
    if strA <= strB:
        return strA+sep+strB
    else:
        return strB+sep+strA

For arbitrarily long lists of strings, either sort the list or generate a set, then concatenate with a separator:

def uniqueStr(sep,strList):
    return sep.join(Set(strList));

Preferably, if the strings are long or the separator choice is a problem, use the hashes and hash the result:

def uniqueStr(sep,strList):
    return hash(''.join([hash(str) for str in Set(strList)]))

Answer 3

You can use x.GetHashCode(). That not ensures that this will be unique, but quite. See more information in this question.

For example:

public int GetUniqueValue(string x, string y)
{
    unchecked {
        var result = x.GetHashCode() * x.GetHashCode();
        return result;
    }
}

Answer 4

Just create a new class and override Equals & GetHashCode:

class StringTuple
{
    public string StringA { get; set; }
    public string StringB { get; set; }

    public override bool Equals(object obj)
    {
        var stringTuple = obj as StringTuple;
        if (stringTuple == null)
            return false;

        return (StringA.Equals(stringTuple.StringA) && StringB.Equals(stringTuple.StringB)) ||
            (StringA.Equals(stringTuple.StringB) && StringB.Equals(stringTuple.StringA));
    }

    public override int GetHashCode()
    {
        // Order of operands is irrelevant when using *
        return StringA.GetHashCode() * StringB.GetHashCode();
    }
}

Answer 5

You could just sort them and concatenate them, along with, lets, say the lenght of the first word.

That way f("one","two") = "onetwo3", f("two","one") = "onetwo3", and no other combination would produce that unique string as , e,g, "onet", "wo" would yield "onetwo4"

However, this will be a abysmal solution for reasonably long strings.

You could also do some sort of hash code calculcation, like this

first.GetHashCode() ^ second.GetHashCode()

that would be reasonably unique, however, you can't guarantee uniqueness.

It would be nice if the OP provided a little more context, because this does not sound like a sound solution to any problem.

Answer 6

Compute a message digest of both strings and XOR the values

MD5(x) ^ MD5(Y)

The message digest gives you unique value for each string and the XOR makes it possible for f(x, y) to be equal to f(y, x).

EDIT: As @Phil H observed, you have to treat the case in which you receive two equal strings as input, which would generate 0 after the XOR. You could return something like an MD5(x+y) if x and y are the same, and MD5(x) ^ MD5(y) for the rest of values.