How to group consecutive similar items of a collection?

Question

Consider the following collection.

• True
• False
• False
• False
• True
• True
• False
• False

I want to display it in a structured way, say, in a TreeView. I want to be able to draw borders around entire groups and such.

• True Group
  • True
• False Group
  • False
  • False
  • False
• True Group
  • True
  • True
• False Group
  • False
  • False

How do I accomplish this with as little procedural code as possible?

Answer 1

This does what you're looking for and is generic:

private static IEnumerable<IGrouping<int, T>> GroupConsecutive<T>(this IEnumerable<T> set, Func<T, T, bool> predicate)
{
    var i = 0;
    var k = 0;
    var ranges = from e in set
                 let idx = ++i
                 let next = set.ElementAtOrDefault(idx)
                 let key = (predicate(e, next)) ? k : k++
                 group e by key into g
                 select g;
    return ranges;
}

Usage:

var set = new List<bool>
            {
                true,
                false,
                false,
                false,
                true,
                true,
                false,
                false,
            };
var groups = set.GroupConsecutive((b1, b2) => (b1 == b2));
foreach (var g in groups)
{
    Console.WriteLine(g.Key);
    foreach (var b in g)
        Console.WriteLine("\t{0}", b);
}

Output:

0
        True
1
        False
        False
        False
2
        True
        True
3
        False
        False