Iterator in aggregate (linq)?

Question

Lets say I have a small integer array like this:

{10,20,30}

Now for the items of that array I want to apply the following formula:

10^(arrayLenght-1) + 20^{arrayLenght-2) + 30^{arrayLenght-3}

Is there a way to accompish this by using the linq aggregate methode though you need some kind of an iterator, which aggregate doesnt implement when I see this right?

Tight

Where are the elements in the array supposed to be used in the formula? It would help if you showed how to do what you want with a for-loop – Herstein

In C#, ^ is XOR, this will affect your return value – Enumerate

^ is supposed to be a power operator here. sry for the confusion – Tight

Answer 1

Here's how I would do it:

array.Select((num, index) => Math.Pow(num, items.Length - index - 1)).Sum();

Tirpitz

Answer 2

Try this:

var a = new int[]{10, 20, 30};
int i = 0;
a.Sum(x => Math.Pow(x, a.Length - ++i));

It uses Sum method because it's more accurate here.

also you can use:

var a = new int[]{10, 20, 30};
a.Select((x,i)=> Math.Pow(x,a.Length-(i+1)));

Arabist

Answer 3

You might try summing the results of a select instead of using aggregate

result = values.Select((t, index) => Math.Pow(t, (values.Length - (index + 1)))).Sum();

Caladium

index starts with 0. – Clime

@Enumerate Yes. Which is what was asked for in the original posting. – Caladium

@Corak. Yep. may bad. Editing – Caladium

Answer 4

The given answers are best to solve this problem, however if you need an aggregate function that exposes the iteration index, you can write your own.

public static TAccumulate Aggregate<TSource, TAccumulate>(
    this IEnumerable<TSource> source,
    TAccumulate seed,
    Func<TAccumulate, TSource, int, TAccumulate> func)
{
    if (source == null)
        throw new ArgumentNullException(nameof(source));

    if (func == null)
        throw new ArgumentNullException(nameof(func));

    var accumulate = seed;
    var i = 0;
    foreach (var item in source)
    {
        accumulate = func(accumulate, item, i);
        i++;
    }
    return accumulate;
}

Reverberator