linq group by contiguous blocks

Question

Let\'s say I have following data:

Time Status
10:00 On
11:00 Off
12:00 Off
13:00 Off
14:00 Off<

Answer 1

You could also do this with one Linq query using a variable to keep track of the changes, like this.

int key = 0;
var query = data.Select(
    (n,i) => i == 0 ? 
        new { Value = n, Key = key } : 
        new 
        { 
            Value = n, 
            Key = n.OnOffFlag == data[i - 1].OnOffFlag ? key : ++key 
        })
    .GroupBy(a => a.Key, a => a.Value);

Basically it assigns a key for each item that increments when the current item does not equal the previous item. Of course this assumes that your data is in a List or Array, otherwise you'd have to try a different method

Answer 2

It can be done as.

1. Iterate over collection.
2. Use TakeWhile<Predicate> condition is text of first element of collection On or Off.
3. Iterate over the subset of from point one and repeat above step and concatenate string.

Hope it helps..

Answer 3

Create a GroupAdjacent extension, such as the one listed here.

And then it's as simple as:

var groups = myData.GroupAdjacent(data => data.OnOffStatus);

Answer 4

Here is a hardcore LINQ solution by using Enumerable.Zip to compare contiguous elements and generate a contiguous key:

var adj = 0;
var t = data.Zip(data.Skip(1).Concat(new TimeStatus[] { null }),
        (x, y) => new { x, key = (x == null || y == null || x.Status == y.Status) ? adj : adj++ }
    ).GroupBy(i => i.key, (k, g) => g.Select(e => e.x));

Answer 5

You could parse the list and assign a contiguous key e.g define a class:

public class TimeStatus
{
    public int ContiguousKey { get; set; }
    public string Time { get; set; }
    public string Status { get; set; }
}

You would assign values to the contiguous key by looping through, maintaining a count and detecting when the status changes from On to Off and so forth which would give you a list like this:

List<TimeStatus> timeStatuses = new List<TimeStatus> 
            {
                new TimeStatus { ContiguousKey = 1, Status = "On", Time = "10:00"},
                new TimeStatus { ContiguousKey = 1, Status = "On", Time = "11:00"},
                new TimeStatus { ContiguousKey = 2, Status = "Off", Time = "12:00"},
                new TimeStatus { ContiguousKey = 2, Status = "Off", Time = "13:00"},
                new TimeStatus { ContiguousKey = 2, Status = "Off", Time = "14:00"},
                new TimeStatus { ContiguousKey = 3, Status = "On", Time = "15:00"},
                new TimeStatus { ContiguousKey = 3, Status = "On", Time = "16:00"}
            };

Then using the following query you can extract the Status and grouped Times:

    var query = timeStatuses.GroupBy(t => t.ContiguousKey)
    .Select(g => new { Status = g.First().Status, Times = g });