Question

I’ve got an IEnumerable<T> containing a list of data elements with consistent intervals in one of the properties:

List<Interval> list = new List<Interval>
            { 
                new Interval{ TIME_KEY = 600},
                new Interval{ TIME_KEY = 605},
                new Interval{ TIME_KEY = 615},
                new Interval{ TIME_KEY = 620},
                new Interval{ TIME_KEY = 630}
            };

How can I query this list (using Linq, preferably), to get a List that looks like this:

 List<Interval> list = new List<Interval>
                { 
                    new Interval{ TIME_KEY = 610},
                    new Interval{ TIME_KEY = 625}
                };

?

EDIT: I will probably know what the interval distance is supposed to be, but if there’s a way to determine it by examing the data, that would be a huge bonus!

EDIT: changed to numeric values

Answer 1

Have a look at this question for an extension method which selects consecutive values. From there, you could do something like:

// I'd probably rename SelectBetween to SelectConsecutive
list.SelectConsecutive((x, y) => new { Original = x, Interval = y - x})
    .Where(pair => pair.Interval != 5)
    .Select(pair => new Interval(pair.Original + 5));

(Somewhat pseudocode, but I hope you see where I’m going.)

However, that would only generate one element when it’s missing… if you went from 0 to 20, it wouldn’t generate 5, 10, 15.

To put some meat on Henk’s second suggestion:

var missing = Enumerable.Range(0, expectedElementCount)
                        .Select(x => new Interval(baseInterval + 5 * x)
                        .Except(list);