Why there is no IndexOf(string value)-like method in Linq?

Question

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Find sequence in IEnumerable<T> using Linq

There is a string method: int IndexOf(string value).
I failed to find a more generic one in Linq, something should look like this:

static int IndexOf<T>(this List<T> source,List<T> value,Predicate<T> equality)

Why Microsoft didn't provide us a generic string search function?

You are contradicting yourself. If it is `string` specific, it is not generic, by definition. — Oded, Nov 20 '11 at 12:46
The word 'string' in the last sentence means a sequence of any kind of data. — TomCaps, Nov 20 '11 at 12:51
No, the word `string` means `string`. Did you mean "a generic collection search function"? — Oded, Nov 20 '11 at 12:54
@Frédéric Hamidi :thansk!this is exactly what I looking for! — TomCaps, Nov 20 '11 at 12:58

Adam Ralph · Accepted Answer · 2011-11-20T13:12:22.730

0

It sounds like your referring to List<T>.FindIndex().

--EDIT--

A more general method for any IEnumerable<T> would be:-

public static int FindIndex<T>(this IEnumerable<T> source, Predicate<T> equality)
{
    return source
        .Select((item, index) => new {Item = item, Index = index})
        .First(x => equality(x.Item)).Index;
}

edited Nov 20 '11 at 13:12

answered Nov 20 '11 at 12:54

Adam Ralph

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Which is `List` specific, not LINQ. – Oded Nov 20 '11 at 12:55
In your 'something should look like this' the extension method parameter is, exactly, `List` – Adam Ralph Nov 20 '11 at 12:56
Good point Adam - guess the OP is contradicting himself on several points. – Oded Nov 20 '11 at 12:58
have edited and added a more general answer – Adam Ralph Nov 20 '11 at 13:12

score 0 · Answer 2 · answered Nov 20 '11 at 13:17

Not a direct answer to your question, but in some cases you do not need to find the index and you can use a function with an index. i think my explanation does not make it any simpler, but maybe an example will make it clearer.

list.Select( (item, index) => /* do something here based on the index of the item */);
list.Where( (item, index) => /* filter the list based on the index and the item */);

Why there is no IndexOf(string value)-like method in Linq?

2 Answers2