CODEWITHSUNDEEP
c#linq
Karsten
Karsten

Reputation: 8144

C#/Linq get sets with adjacent

I have an ordered list like 0,1,2, 6,7, 10

I want to get the sets where the numbers are incremented by 1. I want the first number and the count or the series.

So I would get
start=0, count=3
start=6, count=2
start=10, count=1

How can I do that in C#?

The answer goes to what I feel is the nicest way. Readability is more important than performance for me.

Upvotes: 6

Views: 813

Answers (4)

Reb.Cabin
Reb.Cabin

Reputation: 5567

Try this (as "C# Statements" in LinqPad

var nums = new [] {0, 1, 2, 6, 7, 10};
Debug.Assert(nums.All(i => i >= 0));
Debug.Assert(nums.Zip(nums.Skip(1), (n1, n2) => (n1 < n2)).All(_ => _));
var @group = 0;
nums.Zip(nums.Skip(1).Concat(new [] {nums.Last ()}),
    (n1, n2) => Tuple.Create(
        n1,
        (n2 - n1) == 1 ? @group : @group++))
    .GroupBy (t => t.Item2)
    .Select (g => new {Group = g.Select(x => x.Item1), Count = g.Count()})
    .Dump()
    ;

Upvotes: 2

WaffleSouffle
WaffleSouffle

Reputation: 3363

How about yield ?

class GetSetsWithAdjacent
{
    public struct CountEm
    {
        public int start;
        public int count;

        override public string ToString()
        {
            return string.Format("start={0}, count={1}", this.start, this.count);
        }
    }

    static public IEnumerable<CountEm> GenCount(int[] inputs)
    {
        return GenCount(((IEnumerable<int>)inputs).GetEnumerator());
    }

    static public IEnumerable<CountEm> GenCount(IEnumerator<int> inputs)
    {
        if (inputs.MoveNext())
        {
            CountEm result = new CountEm {start = inputs.Current, count = 1 };

            while (inputs.MoveNext())
            {
                if (result.start + result.count == inputs.Current)
                {
                    result.count += 1;

                }
                else
                {
                    yield return result;
                    result = new CountEm { start = inputs.Current, count = 1 };

                }
            }

            yield return result;
        }
    }
}

class StackOverflow
{
    private static void Test_GetSetsWithAdjacent()
    {
        // http://stackoverflow.com/questions/7064157/c-linq-get-sets-with-adjacent
        int[] inputs = { 0, 1, 2, 6, 7, 10 };

        foreach (GetSetsWithAdjacent.CountEm countIt in GetSetsWithAdjacent.GenCount(inputs))
        {
            Console.WriteLine(countIt);
        }
    }
    internal static void Test()
    {
        Test_GetSetsWithAdjacent();
    }
}

Upvotes: 0

Dean Chalk
Dean Chalk

Reputation: 20451

Maybe it would be neater to use an extension method

public static IEnumerable<IEnumerable<int>> GetConsecutiveCollections(this IEnumerable<int> source)
{
    var list = new List<int>();
    var start = source.Min() - 1;
    foreach (var i in source)
    {
        if (i == start + 1)
        {
            list.Add(i);
            start = i;
        }
        else
        {
            var result = list.ToList();
            list.Clear();
            list.Add(i);
            start = i;
            yield return result;
        }
    }
    yield return list;
}

And then create your result this way:

var result = x.GetConsecutiveCollections()
                .Select(c => new { Start = c.Min(), Count = c.Count()});

Upvotes: 0

Dan Puzey
Dan Puzey

Reputation: 34200

Defining a simple class to hold the results:

    private class Set
    {
        public int Start = 0;
        public int Count = 0;
    }

You can use a method like this:

    private static IEnumerable<Set> GetSets(List<int> src)
    {
        List<Set> rtn = new List<Set>();
        int previous = int.MaxValue;

        foreach (int i in src)
        {
            if (i == previous + 1)
            {
                rtn[rtn.Count - 1].Count += 1;
            }
            else
            {
                rtn.Add(new Set() { Start = i, Count = 1 });
            }

            previous = i;
        }

        return rtn;
    }

I'm not keen on the magic value of int.MaxValue, but it saves extra logic around the first iteration.

Calling GetSets(new List<int>() { 0, 1, 2, 6, 7, 10 }) correctly gives the result you required.

Upvotes: 6

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