CODEWITHSUNDEEP
c#linqc#-4.0
SW Dog
SW Dog

Reputation: 187

Are LINQ Query Expressions Optimized?

Does LINQ do any optimization by sorting/converting data structures?

i.e.

Does LINQ iterate in this code, or is there any type of sorting/conversion done on the data to optimize the find operation?

var list = new List<IdCard> {new IdCard(){Name = "a", Number = 1}, new IdCard() { Name = "b", Number = 2 } };

var idA = list.FirstOrDefault(id => id.Name == "a");
var idB = list.FirstOrDefault(id => id.Name == "b");

I'm trying to understand if my LINQ code is directly translated to an iterative approach. If it is, then it would be better for the above code to use a dictionary lookup (given the case there were to be many look-ups) instead of relying on LINQ, right?

Upvotes: 1

Views: 828

Answers (3)

SW Dog
SW Dog

Reputation: 187

Thank you for your answers! They are very informative.

It looks like the answer for this query is really that some LINQ code may be optimized, and the best way to check is to simply look at the source.

Please correct me if I'm wrong, but the code appears to be available here:

https://github.com/Microsoft/referencesource/blob/master/System.Core/System/Linq/Enumerable.cs

Upvotes: 0

Slai
Slai

Reputation: 22876

No, all System.Linq extensions with predicate parameter enumerate the source collection, and don't modify or optimize the source collection. Some cases such as OrderBy, GroupBy, and Intersect use local collection to prevent enumerating the source more than once.

Lookup (it's similar to Dictionary<K, List<V>>) can be used as an alternative to Dictionary :

var list = new List<IdCard> {new IdCard(){Name = "a", Number = 1}, new IdCard() { Name = "b", Number = 2 } };
var lookup = list.ToLookup(c => c.Name);

var idA = lookup["a"].FirstOrDefault();
var idB = lookup["b"].FirstOrDefault();

Upvotes: -1

Servy
Servy

Reputation: 203835

Does LINQ do any optimization by sorting/converting data structures?

Yes. There are all sorts of optimizations that take place throughout various LINQ methods.

Does LINQ iterate in this code

Yes.

is there any type of sorting/conversion done on the data to optimize the find operation?

No. The work spent constructing an entirely new data structure, in some sorted or hashed manner, would be more work than just iterating the sequence until you find the first item. Creating a collection in the LINQ implementation would not only be more processing work per item (as you're not only executing the predicate, but also whatever work that collection needs to do to store it for later), and using way more memory by storing the items for longer, but you can't quit as soon as you find the match, the way you could with a simple iteration.

then it would be better for the above code to use a dictionary lookup (given the case there were to be many look-ups) instead of relying on LINQ, right?

Yes, that code would be better off if you simply construct the collection using a type that natively provides operations that most effectively do what you want to perform on that collection (in this case, a collection that optimzies searching speed based on a key, so either a dictionary or sorted dictionary), rather than using an improper collection type and using LINQ methods.

Using LINQ is useful when the best algorithm for finding what you want for whatever collection you have (or can have, if you can control what collection you use) is the same as the algorithm you'd use for any arbitrary sequence. That's true in a lot of cases. This isn't one of those cases.

Upvotes: 4

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