Question

If i have two arrays

   First: A, B, C
   Second: ?, B, C

I want to compare only items from Second with items from First which is does not contains question mark “?”.

So for such case:

   First: A, B, C
   Second: ?, B, C

I wan to compare just items 1 and 2 because item 0 in the Second array contains ?.

For that one:

   First: A, B, C
   Second: 2, ?, C

I want to compare only items 0 and 2 because item 1 in Second array contains ?

Any ideas how better and with minimum amount of code to do that? If it would required to create any lists or any another collections that is fine.

Answer 1

Using LINQ from the comfort of your armchair:

// Input data:
var first = new[] { "A", "B", "?" };
var second = new[] { "?", "B", "C" };

// This actually filters out pairs where either first or second
// is equal to "?". If you only want to filter out pairs where the
// second is "?", adjust accordingly.
var toCompare = first.Zip(second, Tuple.Create)
                     .Where(t => t.Item1 != "?" && t.Item2 != "?");

// And now you have a collection of Tuple<string, string>, which
// can be processed in a multitude of ways:
Console.Out.WriteLine(string.Format(
    "Compared {0} items, and found {1} of them equal.",
    toCompare.Count(),
    toCompare.All(t => t.Item1 == t.Item2) ? "all" : "not all"));            

Update:

If the comparison predicate (the method that compares a pair of items and returns a boolean) is going to be more complicated than the above, it makes sense to define it either as a lambda (if it’s not going to be reused and it’s short enough) or as a proper method otherwise.

For example, to implement what’s mentioned in a comment below:

Func<Tuple<string, string>, bool> predicate = t =>
    t.Item2 == "?" ||
    t.Item2 == "_" && t.Item1 != string.Empty ||
    t.Item2 == t.Item1;

// And now you have a collection of Tuple<string, string>, which
// can be processed in a multitude of ways:
Console.Out.WriteLine(string.Format(
    "Compared {0} items, and found {1} of them equal.",
    toCompare.Count(),
    toCompare.All(predicate) ? "all" : "not all"));