How to “zip” or “rotate” a variable number of lists?

Question

If I have a list containing an arbitrary number of lists, like so:

var myList = new List>()
{
    new List() { \"a\",          


        

Answer 1

You can roll your own ZipMany instance which manually iterates each of the enumerations. This will likely perform better on larger sequences than those using GroupBy after projecting each sequence:

public static IEnumerable ZipMany(
    IEnumerable> source,
    Func, TResult> selector)
{
   // ToList is necessary to avoid deferred execution
   var enumerators = source.Select(seq => seq.GetEnumerator()).ToList();
   try
   {
     while (true)
     {
       foreach (var e in enumerators)
       {
           bool b = e.MoveNext();
           if (!b) yield break;
       }
       // Again, ToList (or ToArray) is necessary to avoid deferred execution
       yield return selector(enumerators.Select(e => e.Current).ToList());
     }
   }
   finally
   {
       foreach (var e in enumerators) 
         e.Dispose();
   }
}