C# Check datetime list whether contains linked dates and convert to string

Question

I would like to implement a function somehow like converting the linked dates into string, can refer to the following codes:

List<DateTime> dateList = new List<DateTime>();
dateList.Add(DateTime.Parse("01012021")); // 01 Jan 2021
dateList.Add(DateTime.Parse("02012021")); // 02 Jan 2021
dateList.Add(DateTime.Parse("03012021")); // 03 Jan 2021
dateList.Add(DateTime.Parse("09012021")); // 09 Jan 2021
dateList.Add(DateTime.Parse("10012021")); // 10 Jan 2021
dateList.Add(DateTime.Parse("15012021")); // 15 Jan 2021

And I want a output like: 01 Jan 2021 to 03 Jan 2021, 09 Jan 2021 to 10 Jan 2021, 15 Jan 2021 .

Is there any way/library can be used to complete this function?

Answer 1

There are several ways you can group sequential days. This is just one example, there are likely more efficient approaches if you didn't want invoke Last .

Given

public static IEnumerable<DateTime[]> GetSequential(IEnumerable<DateTime> source)
{
   var temp = new List<DateTime>();
   foreach (var current in source)
   {
      if (temp.Count == 0 || temp.Last().AddDays(1).Date == current.Date)
      {
         temp.Add(current);
         continue;
      }
      yield return temp.ToArray();
      temp.Clear();
      temp.Add(current);
   }
   if(temp.Any())
      yield return temp.ToArray();
}

Usage

var list = new[]
{
   DateTime.ParseExact("01012021", "ddMMyyyy", CultureInfo.InvariantCulture),
   DateTime.ParseExact("02012021", "ddMMyyyy", CultureInfo.InvariantCulture),
   DateTime.ParseExact("03012021", "ddMMyyyy", CultureInfo.InvariantCulture),
   DateTime.ParseExact("09012021", "ddMMyyyy", CultureInfo.InvariantCulture),
   DateTime.ParseExact("10012021", "ddMMyyyy", CultureInfo.InvariantCulture),
   DateTime.ParseExact("15012021", "ddMMyyyy", CultureInfo.InvariantCulture)
};

var results = GetSequential(list)
   .Select(x => x.Count() == 1 ? $"{x.First():dd MMM yyyy}" : $"{x.First():dd MMM yyyy} to {x.Last():dd MMM yyyy}");


Console.WriteLine(string.Join(", ", results));

Output

01 Jan 2021 to 03 Jan 2021, 09 Jan 2021 to 10 Jan 2021, 15 Jan 2021