How to group array of dates into multiple pairs in c#?-CodePudding

In C# trying to figure out the best data structure to group the array of month-end dates into pairs

For instance, my array looks like [2021-09-30,2021-10-31,2021-11-30,2021-12-31] and the output I am expecting is something like below so that I can loop 4 times

[2021-09-30,2021-10-31],[2021-10-31,2021-11-30],[2021-11-30,2021-12-31]

CodePudding user response：

This can be done using the LINQ Aggregate method but it's easier to use the MoreLINQ Pairwise operator:

var dates=new []{
   new DateTime(2021,9,30),
   ...
};

var pairs=dates.Pairwise((a,b)=new {Start=a,End=b});

foreach(var pair in pairs)
{
    var start=pair.Start;
    ...
}

You can use tuples instead of anonymous types to reduce allocations:

var pairs=dates.Pairwise((a,b)=(Start:a,End:b));

foreach(var pair in pairs)
{
    var start=pair.Start;
    ...
}

Pairwise is a small function. You could add it directly to your code instead of installing the MoreLINQ package:

    public static IEnumerable<TResult> Pairwise<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TSource, TResult> resultSelector)
    {
        if (source == null) throw new ArgumentNullException(nameof(source));
        if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));

        return _(); IEnumerable<TResult> _()
        {
            using var e = source.GetEnumerator();

            if (!e.MoveNext())
                yield break;

            var previous = e.Current;
            while (e.MoveNext())
            {
                yield return resultSelector(previous, e.Current);
                previous = e.Current;
            }
        }
    }

Using Zip

Another option is to use Enumerable.Zip to combine the array with itself after skipping one element:

var pairs=dates.Zip(dates.Skip(1),(a,b)=>(Start:a,Start:b));
foreach(var pair in pairs)
{
    var start=pair.Start;
    ...
}

CodePudding user response：

public Dictionary<DateTime, DateTime> GetDatePairs(DateTime[] dateArray)
{
   if (dateArray.Length % 2 != 1)
   {
      throw new ArgumentException($"{nameof(dateArray)} contains an odd number of entries");
   }

   Dictionary<DateTime, DateTime> datepairs = new();

   for (int i = 0; i < dateArray.Length; i  )
   {
      datepairs.Add(dateArray[i], dateArray[i   1]);
      i  ;
   }

   return datepairs;
}