Managing ranges with LINQ challenge

Question

Given the following numbers (representing days of week): 1,2,3,4,5,6,7.

Here are some combination examples and their desired output:

• 1,2,3,5,6,7 -> 1-3,5-7
• 1,3,5,7 -> 1,3,5,7
• 1,2,5,6 -> 1,2,5,6
• 1,2,3,6,7 -> 1-3,6,7

The idea is that 3 or more consecutive days become a range while single or non-following days are rendered separately (or is it nicer to make range starting from 2).

I don't know where to start should I write a complicated ifed function or this can be done with one of the LINQ functions?
Any juicy suggestions?

I used numbers to simplify the idea of ranges, but in my code I have an flagged enum declared as follows:

[Flags]
public enum DaysOfWeek
{
  Sunday = 0x1,
  Monday = 0x2,
  Tuesday = 0x4,
  Wednesday = 0x8,
  Thursday = 0x10,
  Friday = 0x20,
  Saturday = 0x40
}

I have an entity OpeningTimes with a field DaysOfWeek, that tells what days in week the hour-ranges (defined in another property) of this entity apply to.

So the get the above I use (to really get numbers I'd add Select using index + 1):

var days = Enum.GetValues(typeof(DaysOfWeek))
             .Cast<DaysOfWeek>()
             .Where(dow => Model.DaysOfWeek.HasFlag(dow));

I think the idea is to first remove the numbers within a range.

I believe I'm looking for an aggregation function that receives the previous value as well, and can return another value-type, so I can make a function that if current value -1 equals prev. value, I wait for the next value, until range is not consecutive (or if element stands for itself) which is when I yield return the last bulk as an anonymous object and start working on the new one.

Then I'll make a formatting function that says if (item.First != item.Last) string.Join("-", item.First, Item.Last);

Answer 1

Interesting problem. I decided for readability to have a class representing a range:

class NumberRange
{
    public int Start { get; set;}
    public int End { get; set;}
    public override string ToString() 
    {
        return Start == End ? Start.ToString() : String.Format("{0}-{1}",Start,End);
    }
} 

and an extension method to turn an IEnumerable of ordered integers into an IEnumerable of ranges:

public static IEnumerable<NumberRange> ToRanges(this IEnumerable<int> numbers)
{
    NumberRange currentRange = null;
    foreach(var number in numbers)
    {
        if (currentRange == null)
            currentRange = new NumberRange() { Start = number, End = number };
        else if (number == currentRange.End + 1)
            currentRange.End = number;
        else
        {
            yield return currentRange;
            currentRange = new NumberRange { Start = number, End = number };
        }
    }
    if (currentRange != null)
    {
        yield return currentRange;
    }
}

And with that in place you can get the ranges and format them however you want:

String.Join(",",
    new int[] { 1,2,3,5,7,8,9,11 }
        .ToRanges()
        .Select(r => r.ToString()))

Answer 2

Here is what I thought:

void Main()
{
    Console.WriteLine(AggregateString(new int[]{1,2,3,5,6,7}));   //1-3,5-7
    Console.WriteLine(AggregateString(new int[]{1,3,5,7}));       //1,3,5,7
    Console.WriteLine(AggregateString(new int[]{1,2,5,6}));       //1,2,5,6
    Console.WriteLine(AggregateString(new int[]{1,2,3,6,7 }));    //1-3,6,7
}


string AggregateString(int[] ary)
{ 
    List<List<int>> result=new List<List<int>>();
    ary.Aggregate((m,n)=>
        {
            if(m == n-1)
            {
            if(result.LastOrDefault()!=null && result.LastOrDefault().Last() ==m)
                result.Last().Add(n);
            else
                result.Add(new List<int>{m,n}); 
            }
            else 
            {
              if(result.LastOrDefault()==null)
                  result.Add(new List<int>{m,n}); 
              else result.Add(new List<int>{n});
            }
            return n;
        }); 
     return string.Join(",", result.Select(s=>s.Count()>2?
                    string.Join("-",new string[]{s.First().ToString(),s.Last().ToString()}) :
                    string.Join(",",s.Select(x=>x.ToString()).ToArray())).ToArray());
}

Answer 3

Here's my take on it. (Unfortunately, I couldn't prevent duplicating one section:

static IEnumerable<string> GetRange(IEnumerable<int> range)
{
    using(IEnumerator<int> iter = range.GetEnumerator())
    if(iter.MoveNext())
    {
        int last = iter.Current;
        int start = iter.Current;
        while(iter.MoveNext())
        {
            int curr = iter.Current;
            if (curr == last+1)
            {
                last = curr;
                continue;
            }
            // found gap
            if (start == last)   // one isolated value
            {
                yield return start.ToString();
            }
            else if (last - start == 1) // two in a row.
            {
                yield return start.ToString();
                yield return last.ToString();
            }
            else
            {
                yield return string.Format("{0}-{1}", start,last);
            }
            start = curr;
            last = curr;            
        }

        if (start == last)   // one isolated value
        {
            yield return start.ToString();
        }
        else if (last - start == 1) // two in a row.
        {
            yield return start.ToString();
            yield return last.ToString();
        }
        else
        {
            yield return string.Format("{0}-{1}", start,last);
        }
    }
}