Combine multiple collections into a collection of structs with Enumerable?

Question

I have multiple arrays of objects: A, B ,C. They all have the same length.

I want to write a function that "merges" each element of the arrays to single elements in the resuling array.

An example:

(A[0] , B[0] , C[0]) => Result[0]

There is Enumerable.Join(), but my data is not keyed.

Answer 1

Are you looking for Zip? E.g. we can combine items into a named tuple:

var result = A
  .Zip(B, (a, b) => (a, b))
  .Zip(C, (p, c) => (p.a, p.b, c));

E.g.

int[] A = { 1, 2, 3 };
int[] B = { 4, 5, 6 };
int[] C = { 7, 8, 9 };

var result = A
  .Zip(B, (a, b) => (a, b))
  .Zip(C, (p, c) => (p.a, p.b, c));

Console.WriteLine(string.Join(Environment.NewLine, result));

Output:

(1, 4, 7)
(2, 5, 8)
(3, 6, 9)

If you have arbitrary number of arrays you can join items into enumeration of arrays:

private static IEnumerable<T[]> ZipToArray<T>(params IEnumerable<T>[] sources) {
  if (sources is null)
    throw new ArgumentNullException(nameof(sources));

  var ens = sources
    .Select(source => source?.GetEnumerator())
    .ToArray();

  try {
    while (true) {
      foreach (var en in ens)
        if (!(en?.MoveNext() ?? true))
          yield break;

      yield return ens
        .Select(en => en is null ? default(T) : en.Current)
        .ToArray();
      }
  finally {
    foreach (var en in ens)
      en?.Dispose();
  }
}

E.g.

int[] A = { 1, 2, 3 };
int[] B = { 4, 5, 6 };
int[] C = { 7, 8, 9 };

int[][] result = ZipToArray(A, B, C).ToArray();