Question

My question is similar to this one: Finding Consecutive Items in List using Linq. Except, I’d like to get the last consecutive items that have no gaps. For example:

2, 4, 7, 8

output

7,8

Another example:

4,5,8,10,11,12

output

10,11,12

How can that be done?

Answer 1

I’m assuming in that you want the last consecutive sequence with more than one member… so from the sequence

{4, 5, 8, 10, 11, 12, 15} 

you’re expecting the sequence:

{10, 11, 12}

I’ve indicated the line to remove if the last sequence is permitted to have only a single member, giving a sequence of

{15}

Here’s the linq:

new[] {4, 5, 8, 10, 11, 12, 15}
    .Select((n,i) => new {n, i})
    .GroupBy(x => x.n - x.i) //this line will group consecutive nums in the seq
    .Where(g => g.Count() > 1) //remove this line if the seq {15} is expected
    .Select(x => x.Select(xx => xx.n))
    .LastOrDefault()

There’s a hidden assumption here that the numbers of the sequence are in ascending order. If this isn’t the case, it will be necessary to enroll the powers of microsoft’s extension method for finding contiguous items in a sequence. Let me know if this is the case.