LINQ Interview Question #19

What does the Where operator do?

LINQ Fundamentals, Syntax, IEnumerable & IQueryable Junior Beginner

Quick Interview Answer

Where filters a sequence by returning only elements that satisfy a predicate. It does not normally modify the original source.

Detailed Explanation

Where filters a sequence by returning only elements that satisfy a predicate. It does not normally modify the original source.

Where uses deferred execution for IEnumerable<T> and builds a larger expression for IQueryable<T>. Multiple Where calls can be composed when that improves query construction or readability.

Code Example

var adults = people
    .Where(p => p.Age >= 18);

var activeAdults = people
    .Where(p => p.Age >= 18)
    .Where(p => p.IsActive);