Can I use LINQ to compare ranges in two arrays?

Question

I can roll a method, pseudo:

bool Compare(IList left, int lIndex, IList right, int rIndex, int num) { for(int i=0;i<num;++i) { if(left[lIndex+i] != right[rIndex+i]) { return false; } } return true; }

So given L =[1,2,3,4,5,6,7,8] and R = [5,6,7,8,9] : Compare(L,5,R,1,3) == true

I feel I should be able to do a simple LINQ version but I am not sure how to handle the indexing. Can it be written as a trivial LINQ/lambda... otherwise I'll pull this out as a utility method.

By the way there is a question with a very similar title but it is asking a different thing: https://stackoverflow.com/questions/33812323/compare-two-arrays-using-linq

Not at a compiler, but something like Left.Skip(3).Intersect(Right.Skip(1).Take(4))).Count() == 4 — Jaster
– Jaster, Commented Apr 15, 2020 at 14:00

Sweeper · Accepted Answer · 2020-04-15 14:59:26Z

7

You can Skip, Take, and SequenceEqual:

return left.Skip(lIndex).Take(num).SequenceEqual( right.Skip(rIndex).Take(num))

Note that you should make your Compare method generic and use the generic IList<T> instead.

edited Apr 15, 2020 at 14:59

answered Apr 15, 2020 at 14:01

Sweeper

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5 Comments

Mr. Boy Over a year ago

That's neat, thanks. It doesn't matter in my case but does this end up allocating new objects or does each operation return some sort of palce-holder to the original object?

Sweeper Over a year ago

@Mr.Boy It does create new objects that implement IEnumerable, although no new lists are created. They are basically a "view" on your original list. So I would expect this to have more overhead than your for loop.

Mr. Boy Over a year ago

OK but we're talking very light-weight objects designed for this kind of use... so I can live with that. Thankyou.

Pavel Anikhouski Over a year ago

You should keep in mind that it'll work only with generic IList<T>, OP example uses non-generic IList

Mr. Boy Over a year ago

@PavelAnikhouski my code is pseudo but thanks for pointing this out

rachidait · Accepted Answer · 2020-04-15 14:50:17Z

you can try this

 int num = 3,lIndex =5,rIndex =1; var L = (new List<int>(){1,2,3,4,5,6,7,8}).Skip(lIndex).Take(num).ToList(); var R = (new List<int>(){5,6,7,8,9}).Skip(rIndex).Take(num).ToList(); var result = L.Count() == R.Count() && !R.Except(L).Any() && !L.Except(R).Any() && string.Join(",",L).Equals(string.Join(",",R));

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