Using IComparer to compare 2 IEnumerables with 1 comp obj

Question

I'm looking for a way to create a method which should compare for example 2 strings with 1 comparable string and return 1, 0 or -1 (if the value is greater than, equal to, or less than). The method should look like this:

int CompareEnumerables<T>(IEnumerable<T> xs, IEnumerable<T> ys, IComparer<T> comp)

This is the condition: write method (method of general comparison of 2 random sequences (the objects of which are of the same type allowing comparison))

int CompareEnumerables<T>(IEnumerable<T> xs, IEnumerable<T> ys, iComparer<T> comp)

to return -1, 0 or 1 depending on which a series of lexicographical precedes the other.

Any idea how to do so? I tried a few times. If needed I will share code.

I'm not clear on what you want here. What should the method return and why? — ProgrammingLlama, Sep 16 '21 at 11:27
So you are looking for SequenceEqual? https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.sequenceequal?view=net-5.0 — Rand Random, Sep 16 '21 at 11:27
The method should return 1, 0 or -1 (if the value is greater than, equal to, or less than) - by that I think its about the string length. And by looking at the documentation for IComparer it should use the method Compare. — RRuseva, Sep 16 '21 at 11:32
What did you try ? If you show us what you tried, it is easier to understand your requirements. And maybe we can show you where your attempt failed. — AndrewR, Sep 16 '21 at 11:42
"abc","bwe" should return 0 (equal). From the documentation for IComparer.Compare those values can be seen. however my method should have for example: "abc", "bwe" as the two strings and "mnb" as a string to use to compare. In this case the result should be again 0 — RRuseva, Sep 16 '21 at 11:42
https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.icomparer-1.compare?view=net-5.0 — RRuseva, Sep 16 '21 at 11:43
So "abc","bwe" are equal? I dont understand that or how the IComparer plays into that. — Magnus, Sep 16 '21 at 11:44
Yes, they are equal because there are 3 letters in each of them — RRuseva, Sep 16 '21 at 11:45
public static int CompareEnumerables (IEnumerable xs, IEnumerable ys, IComparer comp) { List listToCompare1 = new List(xs); List listToCompare2 = new List(ys); return Comparer.DefaultInvariant.Compare(listToCompare1, listToCompare2); } - this is the first code that I tried — RRuseva, Sep 16 '21 at 11:46
But what do you use the IComparer for if you are just comparing lengths? — Magnus, Sep 16 '21 at 11:48
Mabay you should just post the entire requirement as given to you in the question. — Magnus, Sep 16 '21 at 11:54

score 0 · Answer 1 · answered Sep 16 '21 at 12:25

How about something like this:

public class SequenceComparer<T> : IComparer<IEnumerable<T>>
{
    public SequenceComparer(IComparer<T> inner = default)
    {
        Inner = inner ?? Comparer<T>.Default;
    }
    
    public IComparer<T> Inner { get; }
    
    public int Compare(IEnumerable<T> left, IEnumerable<T> right)
    {
        if (left is null) throw new ArgumentNullException(nameof(left));
        if (right is null) throw new ArgumentNullException(nameof(right));
        
        using (var leftEnum = left.GetEnumerator())
        using (var rightEnum = right.GetEnumerator())
        {
            bool leftRunning = leftEnum.MoveNext();
            bool rightRunning = rightEnum.MoveNext();
            while (leftRunning && rightRunning)
            {
                int result = Inner.Compare(leftEnum.Current, rightEnum.Current);
                if (result != 0) return result;
                
                leftRunning = leftEnum.MoveNext();
                rightRunning = rightEnum.MoveNext();
            }
            
            if (leftRunning) return 1;
            if (rightRunning) return -1;
            return 0;
        }
    }
}

static int CompareEnumerables<T>(IEnumerable<T> xs, IEnumerable<T> ys, IComparer<T> comp)
{
    var comparer = new SequenceComparer<T>(comp);
    return comparer.Compare(xs, vs);
}

Using IComparer to compare 2 IEnumerables with 1 comp obj

1 Answers1