How to Get the Index of an Element in a List or Array Using LINQ?

Efficiently Finding Element Indices Using LINQ

Working with data structures like lists and arrays often requires locating the index of an element that matches specific criteria. LINQ offers an elegant solution, providing concise and readable code compared to traditional loop-based approaches.

To pinpoint the index of the first element meeting a condition, consider this LINQ query:

<code class="language-csharp">myCars
    .Select((car, index) => new { car, index })
    .First(myCondition)
    .index;</code>

This code first uses Select to create anonymous objects, pairing each car with its index. First then filters this sequence, returning the first object satisfying myCondition. Finally, the index property of this object reveals the desired index.

A slightly more compact version:

<code class="language-csharp">myCars
    .Select((v, i) => new { car = v, index = i })
    .First(myCondition)
    .index;</code>

Further simplification is possible using C# 7 tuples:

<code class="language-csharp">myCars
    .Select((car, index) => (car, index))
    .First(myCondition)
    .index;</code>

The benefit of using LINQ is clear: it delivers clean, expressive code, eliminating the need for manual iteration and explicit variable management.

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