If statement or Where extension with a For Each loop?

I was wondering which of the two code samples would be more efficient (or is 开发者_运维百科the difference between the two negligible)?

For Each apple in AppleController.GetRedApples().Where(Function(a) PriceController.OnSale(a))
   'do something
Next

or

For Each apple in AppleController.GetRedApples()
   If PriceController.OnSale(apple) Then
      'do something
   End If
Next

Thanks!

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The difference is negligible, and the second code is much more readable, so you should probably prefer that one

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I would personally separate it out:

Dim applesOnSale = AppleController.GetRedApples() _
                                  .Where(Function(a) PriceController.OnSale(a))
For Each apple in applesOnSale
   'do something
Next

In a full IDE the first part could be a single line - or you could use a VB query expression like this:

Dim applesOnSale = From apple in AppleController.GetRedApples() _
                   Where PriceController.OnSale(apple)

For Each apple in applesOnSale
   'do something
Next

This separates the "what items you're interested in" from "what you want to do with the items" which I personally find useful in terms of readability.

Note that in some situations the Where may not work, however - if GetRedApples returns a table from a LINQ to SQL DataContext, for example, it will try to translate the Where clause into SQL - which won't work.

Assuming you're using LINQ to Objects though, the assignment won't actually do any looping - it will just set up the query. The "where" clause will only be evaluated for each item as you loop through the query.

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Consider this discussion on foreach vs linq/lambda (also answer by Jon Skeet ;-) and this one if you want to delve deeper into understanding LINQ / Lambda efficiency and performance.

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The performance should be about the same, therefore I would go for the more readable approach:

var applesOnSale = from apple in AppleController.GetRedApples()
                   where PriceController.OnSale(apple)
                   select apple;

foreach(var apple in applesOnSale)
{
    //do stuff
}

This is the same as your second option but is a touch more readable.