C# arrays: finding custom minimal element

Question

How do I specify a custom code for comparison when finding a minimal element in my Array?

For example, I have two arrays:

int[] a = new int[] {3, 6, 8};
int[] b = new int[] {9, -2, 5};

I want to figure out, what would be the minimal ratio of the elements with respective indexes (i.e. find minimum of 3/9, 6/(-2) and 8/5) and then return the index. I'm already aware of Array.Min(), but I wonder if it's possible to make any sort of it's customization.

Answer 1

Perhaps something like this:

double smallest = double.MaxValue;
int smallestIndex = 0;

for (int i = 0; i < (a.Length > b.Length ? b.Length : a.Length); i++)
{
    if ((double)a[i] / b[i] < smallest)
    {
        smallest = (double)a[i] / b[i];
        smallestIndex = i;
    }
}

smallestIndex will contain the index of the smallest ratio at the end.

Answer 2

with linq you could do this:

            int customMin = a.Select((v, i) => new { a = v, b = b[i] })
                .Select(x => x.a / x.b)
                .Min();

the first select merges the two lists into on, the second select calculates your custom mertic, then we call min to get the minimum.

Answer 3

Using linq to get the minimal value AND the index, you could look at this answer:

http://stackoverflow.com/questions/914109/how-to-use-linq-to-select-object-with-minimum-or-maximum-property-value

Using Jon Skeet extension method, you could then write

var result = Enumerable.Range(0,a.Length)
     .Select(i => new {Value = a[i]/b[i], Index = i})
     .MinBy(r => r.Value);

(you'll have to watch out for 0's in b)

Answer 4

You could use linq to 'zip' the two sequences together, order them by their ratio and select the first index:

a.Select((item, index) => {new { A = item, B = b[index], Idx = index })
    .OrderBy(i => (double)i.A / i.B)
    .Select(i => i.Idx)
    .First();

Answer 5

don't forget about the SortedList Class