Can we use multiple variables in foreach

Question

Can we use multiple variables in foreach

foreach (var item1 in collection1;var items2 in collection2)
{

}

I want to do this because I need to fetch two collections from a database and append both of them to a ComboBox.

Answer 1

Use LINQ to join the arrays putting the result into an anonymous type, then iterate over the resulting collection.

var col = collection1.Join(collection2, x => x, y => y, (x, y) => new { X = x, Y = y });
foreach (var entry in col) {
    // entry.X, entry.Y
}

Edit:

When posting the answer I assumed that collection1 and collection2 contained different types. If they contain both the same type or share a common base type, there are alternatives:

If you want to allow duplicates:

collection1.Concat(collection2); // same type
collection1.select(x => (baseType)x).Concat(collection2.select(x => (baseType)x)); // shared base type

No duplicates:

collection1.Union(collection2); // same type
collection1.select(x => (baseType)x).Union(collection2.select(x => (baseType)x)); // shared base type

Form framework 4.0 onwards Zip can replace the original solution:

collection1.Zip(collection2, (x, y) => new { X = x, Y = y });

For an overview over most of the available LINQ funktions please refer to 101 LINQ Samples.

Without LINQ use two hierarchical foreach loops (increasing the number of interations) or one foreach loop to create an inermediate type and a second to iterate over the collection of intermediates or if the types in the collections are the same add them to a list (using AddRange) and then iterate over this new list.

Many roads lead to one goal ... its up to you to chose one.

Answer 2

You can Zip the collections

foreach (var item in collection1.Zip(collection2, (a, b) => new {  A = a, B = b }))
{
  var a = item.A;
  var b = item.B;
  // ...
}

This assumes that the elements match at the same position (e.g. the first element from collection1 joins the first element of collecion2). It is quite efficient.