連続する数値を識別

Extension.cs

[TestFixture]
static class Extensions {
	public static string RangeString(this IEnumerable<int> src) {
		var grouped = src.RangeGroup()
				.Select(x => x.Item1 == x.Item2 ?
					x.Item1.ToString() :
					string.Format("{0} ... {1}", x.Item1, x.Item2));


		var create = grouped.Aggregate("", (s, x) => string.Format("{0}{1},", s, x));
		return create.Substring(0, create.Length - 1);//deliminator
	}
	/// <summary>
	/// 連続する数値の開始と終了の数値のタプルを返します
	/// </summary>
	/// <param name="src"></param>
	/// <returns></returns>
	public static IEnumerable<Tuple<int, int>> RangeGroup(this IEnumerable<int> src) {
		int start = int.MinValue;
		int recent = int.MinValue;
		foreach (var ch in src.OrderBy(x => x).Distinct()) {
			if (start == int.MinValue) {
				//開始点
				start = ch;
				recent = ch;
			} else if (recent == ch - 1) {
				//中間 
				recent = ch;
			} else {
				//終点
				yield return new Tuple<int, int>(start, recent);
				start = ch;
				recent = ch;
			}
		}
		yield return new Tuple<int, int>(start, recent);
	}

	[Test]
	public static void RangeStringTest() {
		var str = new[] { 1, 5, 6, 7, 10, 15, 16, 17, 18, 19 }.ChannelString();

		Console.WriteLine(str);
		Assert.AreEqual("1,5 ... 7,10,15 ... 19", str);
	}
}