Find index of a value in an array

Question

Can linq somehow be used to find the index of a value in an array?

For instance, this loop locates the key index within an array.

for (int i = 0; i &         


        

Answer 1

For arrays you can use: Array.FindIndex:

int keyIndex = Array.FindIndex(words, w => w.IsKey);

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For lists you can use List.FindIndex:

int keyIndex = words.FindIndex(w => w.IsKey);

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You can also write a generic extension method that works for any Enumerable:

///
Finds the index of the first item matching an expression in an enumerable.
///The enumerable to search.
///The expression to test the items against.
///The index of the first matching item, or -1 if no items match.
public static int FindIndex(this IEnumerable items, Func predicate) {
    if (items == null) throw new ArgumentNullException("items");
    if (predicate == null) throw new ArgumentNullException("predicate");

    int retVal = 0;
    foreach (var item in items) {
        if (predicate(item)) return retVal;
        retVal++;
    }
    return -1;
}

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And you can use LINQ as well:

int keyIndex = words
    .Select((v, i) => new {Word = v, Index = i})
    .FirstOrDefault(x => x.Word.IsKey)?.Index ?? -1;