How can I group by the difference between rows in a column with linq and c#?

Question

I want to create a new group when the difference between the values in rows are greater then five.

Example:

int[] list = {5,10,15,40,45,50,70,75};

should give me 3 groups:

1,[ 5,10,15 ]
2,[40,45,50]
3,[70,75]

Is it possible to use Linq here?

Thx!

Answer 1

Exploiting side effects (group) is not a good practice, but can be helpful:

  int[] list = { 5, 10, 15, 40, 45, 50, 70, 75 };

  int step = 5;
  int group = 1;

  var result = list
    .Select((item, index) => new {
               prior = index == 0 ? item : list[index - 1],
               item = item,
             })
    .GroupBy(pair => Math.Abs(pair.prior - pair.item) <= step ? group : ++group, 
             pair => pair.item);

Test:

  string report = string.Join(Environment.NewLine, result
    .Select(chunk => String.Format("{0}: [{1}]", chunk.Key, String.Join(", ", chunk))));

Outcome:

1: [5, 10, 15]
2: [40, 45, 50]
3: [70, 75]

Answer 2

Assuming collection has an indexer defined, can be something like this:

const int step = 5;
int currentGroup = 1;
var groups = list.Select((item, index) =>
{
    if (index > 0 && item - step > list[index - 1])
    {
        currentGroup++;
    }
    return new {Group = currentGroup, Item = item};
}).GroupBy(i => i.Group).ToList();