C# Custom Sort String IComparer

Question

I want to change the sorting of strings so it is based off the following alphabet:

A,E,I,O,U,F,G,L,M,N,P,S,T,V,H,K,R

Instead of the standard A,B,C,D ... X,Y,Z

So I started to try and create a IComparer but stuck on how to implement.

Here is what I got so far which ain't much.

public class CustomSort : IComparer<string>
{
    public int Compare(string a, string b)
    {
        return 1;
    }
}

Any help would be much appreciated.

@xanatos It would appear SamoanProgrammer's instructor has done the former and SP is trying to do the latter. :roll: — ruffin
– ruffin, Commented Apr 11, 2017 at 12:28

xanatos · Accepted Answer · 2017-04-11 12:22:52Z

3

It should be something very like this:

In the end you compare character by character, finding the "index" of the character inside a Order string. Perhaps to speed it up you could convert the Order string to a Dictionary<char, int> where the int is the "weight".

public class CustomSort : IComparer<string>
{
    public const string Order = "AEIOUFGLMNPSTVHKR";

    public int Compare(string a, string b)
    {
        if (a == null)
        {
            return b == null ? 0 : -1;
        }

        if (b == null)
        {
            return 1;
        }

        int minLength = Math.Min(a.Length, b.Length);

        for (int i = 0; i < minLength; i++)
        {
            int i1 = Order.IndexOf(a[i]);
            int i2 = Order.IndexOf(b[i]);

            if (i1 == -1)
            {
                throw new Exception(a);
            }

            if (i2 == -1)
            {
                throw new Exception(b);
            }

            int cmp = i1.CompareTo(i2);

            if (cmp != 0)
            {
                return cmp;
            }
        }

        return a.Length.CompareTo(b.Length);
    }
}

answered Apr 11, 2017 at 12:22

xanatos

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7 Comments

SamoanProgrammer Over a year ago

Hi xanatos, thank you very much. That has done exactly what I needed to do :) Awesome work mate!

juharr Over a year ago

So comparing "Hello There" to "HelloWorld" is going to thrown an exception, but comparing "Hello There" and "Hello" will not.

xanatos Over a year ago

@juharr Yep :-) I don't do a correctness check on the whole string.

juharr Over a year ago

Actually both throw since you only deal with upper case characters. I guess as long as the strings only contain upper case A-Z this is good enough, but should be noted.

SamoanProgrammer Over a year ago

Yeah, I found I got an exception with lower case characters but I fixed that up and spaces, but the bulk of what I needed done was handled as I wanted :)

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