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C# Querying With LINQ Query Operators Quantifiers

Posted by codey code
codey code
168 Points

Shouldn't the methods Any() and All() have the same efficiency?

Suppose if in our Birds List, we have 5th element as Sparrow, then birds.Any(b => b.Name == "sparrow") returns true for 5th element and stops further evaluation

In the second case, birds.All(b => b.Name != "sparrow") returns false for the 5th element and stops further evaluation.

So, according to this, both of them have the same efficiency. Am I missing something?

2 Answers

Steven Parker
Steven Parker
229,732 Points
Steven Parker
Steven Parker
229,732 Points

The efficiency is different if you use the same condition.

Since you're using different conditions, you've effectively made them equivalent in efficiency. But for the same condition, Any can return a true as soon as it finds a single item, but All cannot return true until it has examined every item.

Luis Marsano
Luis Marsano
21,425 Points
Luis Marsano
Luis Marsano
21,425 Points

Am I missing something?

No, and what you've observed is De Morgan's Law: for any predicate p, enumerable.All(x => !p(x)) is logically equivalent to !enumerable.Any(p). Both expressions short-circuit for precisely the same enumerable and predicate p (ie, as soon as p(x) is true).

You make a good point: for a given predicate p, you don't have much choice between quantifiers: you must choose between logically equivalent formulations, which also short-circuit identically. Any situation where enumerable.Any(p) is right, enumerable.All(p) is likely wrong. The presentation was a bit misleading in that respect. However, if you have a choice among predicates, then any predicate that short-circuits a quantifier expression will also short-circuit the other logically equivalent quantifier expression. So, just choose good predicates.