Question

I like anonymous lambdas; they let you concisely express complex selects from lists. LINQ does something similar, so I thought I’d try it out (finally).

As someone who uses lambdas often to select subsets of collections, when should I use LINQ and when should I use lambdas? There are questions like this one which show a 10-100x difference in performance one way or the other.

Answer 1

LINQ evaluation is deferred. The expression for primes and numbers.Where(n => isOddAndNotDivisibleBy(n)) are identical to the compiler. In both cases, isOddAndNotDivisibleBy is never called until something evaluates a result of the expression. In this case, the ToArray between c and b forces the evaluation. If you added ToArray between a and b, you’d get similar times.

for comparison you could try:

var primes = (
    from n in numbers
    where isOddAndNotDivisibleBy(n)
    select n).ToArray();