Question

I got in a discussion with two colleagues regarding a setup for an iteration over an IEnumerable (the contents of which will not be altered in any way during the operation). There are three conflicting theories on which is the optimal approach. Both the others (and me as well) are very certain and that got me unsure, so for the sake of clarity, I want to check with an external source.

The scenario is as follows. We had the code below as a starting point and discovered that some of the hazaas need not to be acted upon. So, starting with the code below, we started to add a blocker for the action.

foreach(Hazaa hazaa in hazaas) ;

My suggestion is as follows.

foreach(Hazaa hazaa in hazaas.Where(element => condition)) ;

One of the guys wants to resolve it by a more explicit form, claiming that LINQ is not appropriate in this case (not sure why it’d be so but he seems to be very convinced). He’s solution is this.

foreach(Hazaa hazaa in hazaas) ;
  if(condition) ;

The other contra-suggestion is supported by the claim that Where risks to repeat the filtering process needlessly and that it’s more certain to minimize the computational workload by picking the appropriate elements once for all by Select.

foreach(Hazaa hazaa in hazaas.Select(element => condition)) ;

I argue that the first is obsolete, since LINQ can handle data objects quite well.

I also believe that Select-ing is in this case equivalently fast to Where-ing and no needless steps will be taken (e.g. the evaluation of the condition on the elements will only be performed once). If anything, it should be faster using Where because we won’t be creating an extra instance of anything.

Who’s right?

Answer 1

Select is inappropriate. It doesn’t filter anything.
if is a possible solution, but Where is just as explicit.
Where executes the condition exactly once per item, just as the if. Additionally, it is important to note that the call to Where doesn’t iterate the list. So, using Where you iterate the list exactly once, just like when using if.

I think you are discussing with one person that didn’t understand LINQ – the guy that wants to use Select – and one that doesn’t like the functional aspect of LINQ.

I would go with Where.