Apply function to all elements of collection through LINQ [duplicate]

Answer 1

For collections that do not support ForEach you can use static ForEach method in Parallel class:

var options = new ParallelOptions() { MaxDegreeOfParallelism = 1 };
Parallel.ForEach(_your_collection_, options, x => x._Your_Method_());

Answer 2

The idiomatic way to do this with LINQ is to process the collection and return a new collection mapped in the fashion you want. For example, to add a constant to every element, you'd want something like

var newNumbers = oldNumbers.Select(i => i + 8);

Doing this in a functional way instead of mutating the state of your existing collection frequently helps you separate distinct operations in a way that's both easier to read and easier for the compiler to reason about.

If you're in a situation where you actually want to apply an action to every element of a collection (an action with side effects that are unrelated to the actual contents of the collection) that's not really what LINQ is best suited for, although you could fake it with Select (or write your own IEnumerable extension method, as many people have.) It's probably best to stick with a foreach loop in that case.