Init array of type with lambda

Question

class A
{
        private int p;

        public A(int a)
        {
            p = a;
        } 
}

int[] n = { 1, 2, 3, 4, 5 };

how to make an array of A initialized with values from n using lambda. Its ok to use lambda for that?

To be picky about the wording: Lambda is only the nice syntax for writing an "inline"/anonymous function like i => new A(i). To use the lambda you must call it or pass it to a method that calls the lambda. LINQ contains many suitable methods for dealing with collections, many of them is preferably called with lambdas as arguments. Your question would make more sense if you replaced "lambda" with LINQ. — Albin Sunnanbo
– Albin Sunnanbo, Commented Mar 20, 2011 at 12:43

Albin Sunnanbo · Accepted Answer · 2011-03-20 12:43:46Z

4

I prefer the LINQ query syntax (there is a lambda behind the scenes but hidden behind syntactic sugar).

(
    from i in n
    select new A(i)
).ToArray();

But you can use the explicit LINQ syntax where you type out the lambda.

n.Select(i => new A(i)).ToArray();

edited Mar 20, 2011 at 12:43

answered Mar 20, 2011 at 12:37

Albin Sunnanbo

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2 Comments

xanatos Over a year ago

+1 I prefer the second one... With a "general" caveat... If the array is VERY big, please don't do this. ToArray will create a List<T> and then from the List an Array. So it'll waste uselessly much memory (the List).

Albin Sunnanbo Over a year ago

@xanatos, At least in .NET4 Enumerable.ToArray<T> creates a Buffer<T> and not a List<T> internally. Nevertheless there might be one extra copy step in ToArray<T> compared to ToList<T> if the final array length is not a power of 2. But until profiling has proven that is your problem you don't need to worry about it.

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