Convert existing snippet of code to use Array.ForEach

Question

We know that if you have:

var aa = new [] { 1, 2, 3, 4, 5 };
for (int i = 0; i < aa.length; ++i)
{
    aa[i] = aa[i] + 1;
}

it's really

var aa = new [] { 1, 2, 3, 4, 5 };
Arrary.ForEach(aa, a => a + 1);

However, what if I had this:

var aa = new [] { 1, 2, 3, 4, 5 };
var ab = new [] { 1, 2, 3, 4, 5 };
for (int i = 0; i < aa.length; ++i)
{
    aa[i] = ab[i] + 1;
}

Can I convert this to use just one Array.ForEach? Or, how would you do it, if you wanna go all functional programming crazy? Clunky for loops just looks ugly.

Answer 1

This won't be fast, but it just might work

var aa = new [] { 1, 2, 3, 4, 5 };
var ab = new [] { 1, 2, 3, 4, 5 };
Array.ForEach(aa, new Action(a => ab[Array.IndexOf(a)] + 1));

Unfortunately thiswill not work for an array with duplicate elements.

Answer 2

It's not pretty, but this will work (using the Select() overload that returns the index of the element):

var aa = new[] { 1, 2, 3, 4, 5 };
var ab = new[] { 1, 2, 3, 4, 5 };

Array.ForEach(
    aa.Select((x, i) => i).ToArray(),
    i => aa[i] = ab[i] + 1);

IMHO a simple "for" loops is a lot easier to understand in this case.

Answer 3

Another similar approach:

Enumerable.Range(0, ab.Length).Select(i => aa[i] = ab[i] + 1);
// Will not work if aa.Length != ab.Length

Answer 4

How about:

aa = ab.ConvertAll(x => x+1);

Answer 5

Not a direct answer, but you want ForEach2, which iterates over two sequences/arrays. Unfortunately this is not included with the BCL, so you'll have to add it.

But if you're trying to do functional in C#, you'll probably have a helper library anyways, so it's not that big of a deal.

Answer 6

var aa = new[] { 1, 2, 3, 4, 5 };
var ab = new[] { 1, 2, 3, 4, 5 };

var index = 0;
Array.ForEach(aa, a => { aa[index] = ab[index] + 1; index++; });

Would this not work? Its 1 Array.ForEach with the indexer held outside of the Array.ForEach.