How to group a list of integers based on moving range?

Question

I have a

list<int> = {14, 24, 56,189,909,1000};

I want to collapse (group?) them by a range such that the ints that fall within the range of each other are collapse into one value.

So the results should be for range = 100

{14,24,56} //since they 24 falls within 100 of 14 and 56 falls within 100 of 24
{189}
{909, 1000} //since they fall within 100 of each other

I know this is possible using a linq group by but I am stumped by the syntax.

I have looked at this answer but cannot figure out what to use for the ranges, since I have only one range i.e. 100.

int[] values = {100, 110, 120, 130, 140, 150, 160, 170};
        int[] ranges = {115, 145, 180};

    var query = from value in values
                group value by ranges.Where(x => value >= x)
                                     .DefaultIfEmpty()
                                     .Last();

    foreach (var group in query)
    {
        Console.WriteLine("{0}: {{{1}}}", group.Key, 
                          string.Join(", ", group));
    }

What would the result be if there was 150 in the input? Would it be part of the first or second group? — user2864740, Sep 29 '14 at 22:10
sorry missed your question, if it's 150, it would be in both sets. {14,24,56, 150}, {150, 189}. Thanks. — Santino, Sep 29 '14 at 22:12
Then why is 189 not also part of the first set (as 189 is less than 150 + 100)? — user2864740, Sep 29 '14 at 22:21
You are correct 189 should also be in the first set. sorry been a long day :-/ — Santino, Sep 29 '14 at 22:29

user2864740 · Answer 1 · 2014-09-29T22:22:15.533

Edit: This may not apply, especially with the additional requirement in the comment as it 1) starts each group only at one point and 2) would place 150 only in the first group.

I would probably write it as so because of the "dynamic" range (and I'm not sure how Group By could be used without an equally involved bucket process). This function requires that the input is already sorted.

IEnumerable<IEnumerable<int>> GroupByStartingRange (IEnumerable<int> src) {
    int? maybeStart;
    while ((maybeStart = src.FirstOrDefault() != null) {
       if (maybeStart.HasValue) {
          var start = maybeStart.Value;
          yield return src.TakeWhile(x => x <= start + 100)
          src = src.SkipWhile(x => x <= start + 100);
       }
    }
}

score 1 · Accepted Answer · answered Sep 29 '14 at 22:24

Your best option is using a plain old for loop instead of linq:

            var l = new[] { 14, 24, 56, 189, 909, 1000 };
            var groups = new List<List<int>>();
            groups.Add(new List<int>());
            groups[0].Add(l[0]);
            for (int i = 1; i < l.Length; i++)
            {
                if (l[i] - l[i - 1] > 100)
                {
                    groups.Add(new List<int>());
                }
                groups[groups.Count - 1].Add(l[i]);
            }

Thanks, this did it. Got me out of the fancy schmancy Linq stuff and do it plain old way. Much appreciated — Santino, Sep 29 '14 at 22:44

score 0 · Answer 3 · answered Sep 29 '14 at 22:11

0

Assuming your ranges are ordered:

int[] values = { 100, 110, 120, 130, 140, 150, 160, 170 };
int[] ranges = { 115, 145, 180 };
var groups = values.GroupBy(x => ranges.First(r => x <= r));

answered Sep 29 '14 at 22:11

atlanteh

5,615
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2

`r => x <= r` looks really funny. – Mephy Sep 29 '14 at 22:15
actually I have 1 range, but that's ok can use your code with just a single element array. – Santino Sep 29 '14 at 22:16

How to group a list of integers based on moving range?

3 Answers3