in linq why are subsequent calls of IEnumerable.Intersect so much faster

Question

while looking at this question C# Similarities of two arrays it was noted that the initial linq call was significantly slower than subsequent calls. What is being cached th

Answer 1

LINQ heavily uses deferred execution. Unless you enumerate a query, it does not get executed.

Change

 s.Start();
 z= a.Intersect(b);
 s.Stop();

to

 s.Start();
 z= a.Intersect(b).**ToArray**();
 s.Stop();

and please post the new performance results.

a.Intersect(b) represents an expression, independent of the value of a and b. Values of a and b are only used when the expression is evaluated by enumeration.