Creating N objects and adding them to a list

Question

I have a method which takes in N, the number of objects I want to create, and I need to return a list of N objects.

Currently I can do this with a simple loop:

    private static IEnumerable<MyObj> Create(int count, string foo)     {         var myList = new List<MyObj>();          for (var i = 0; i < count; i++)         {             myList .Add(new MyObj                 {                     bar = foo                 });         }          return myList;     } 

And I'm wondering if there is another way, maybe with LINQ to create this list.

I've tried:

    private static IEnumerable<MyObj> CreatePaxPriceTypes(int count, string foo)     {         var myList = new List<MyObj>(count);          return myList.Select(x => x = new MyObj             {                 bar = foo             });      } 

But this does seem to populate my list.

I tried changing the select to a foreach but its the same deal.

I realized that the list has the capacity of count and LINQ is not finding any elements to iterate.

        myList.ForEach(x => x = new MyObj         {             bar = foo         }); 

Is there a correct LINQ operator to use to get this to work? Or should I just stick with the loop?

Answer 1

You can use the Range to create a sequence:

return Enumerable.Range(0, count).Select(x => new MyObj { bar = foo }); 

If you want to create a List, you'd have to ToList it.

Mind you though, it's (arguably) a non-obvious solution, so don't throw out the iterative way of creating the list just yet.

Answer 2

You could create generic helper methods, like so:

// Func<int, T>: The int parameter will be the index of each element being created.  public static IEnumerable<T> CreateSequence<T>(Func<int, T> elementCreator, int count) {     if (elementCreator == null)         throw new ArgumentNullException("elementCreator");      for (int i = 0; i < count; ++i)         yield return (elementCreator(i)); }  public static IEnumerable<T> CreateSequence<T>(Func<T> elementCreator, int count) {     if (elementCreator == null)         throw new ArgumentNullException("elementCreator");      for (int i = 0; i < count; ++i)         yield return (elementCreator()); } 

Then you could use them like this:

int count = 100;  var strList = CreateSequence(index => index.ToString(), count).ToList();  string foo = "foo"; var myList = CreateSequence(() => new MyObj{ Bar = foo }, count).ToList();