C# - ElementAtOrDefault Use

ElementAtOrDefault. The C# ElementAtOrDefault method accesses an element. It handles an out-of-range access without throwing an exception.

ElementAtOrDefault returns a default value if the index is not present. ElementAt meanwhile will throw an error on nonexistent indexes.

Exception

LINQ

Example. In this program we create a 3-element array. The only valid indexes to access are 0, 1 and 2. We show how ElementAtOrDefault works on valid indexes, and also out-of-range indexes.

int Array

Tip On out-of-range accesses, ElementAtOrDefault returns the default value for the type, which for int is 0.

int

default

using System; using System.Linq; int[] array = { 4, 5, 6 }; // Call ElementAtOrDefault with various indexes. int a = array.ElementAtOrDefault(0); int b = array.ElementAtOrDefault(1); int c = array.ElementAtOrDefault(-1); int d = array.ElementAtOrDefault(1000); Console.WriteLine(a); Console.WriteLine(b); Console.WriteLine(c); Console.WriteLine(d);

4 5 0 0

ElementAt. This method gets an element at an index. In many IEnumerable types, you cannot directly index a certain element. ElementAt can help with these types.

Here This program uses an array of 3 string literal elements. Arrays are IEnumerable collections.

Array

IEnumerable

And We can index this array through the ElementAt method in the System.Linq namespace.

Warning The method call with argument 3 throws a System.ArgumentOutOfRangeException.

ArgumentException

using System; using System.Linq; // Input array. string[] array = { "Dot", "Net", "Perls" }; // Test ElementAt for 0, 1, 2. string a = array.ElementAt(0); Console.WriteLine(a); string b = array.ElementAt(1); Console.WriteLine(b); string c = array.ElementAt(2); Console.WriteLine(c); // This is out of range. string d = array.ElementAt(3);

Dot Net Perls Unhandled Exception: System.ArgumentOutOfRangeException: Index was out of range.

Index from end. With the "^" syntax, we can access an index from the end of a collection. So "^2" will get the second-to-last element.

Note This syntax is the same as the end-indexing syntax available for lists and arrays in C#.

using System; using System.Linq; var values = new char[] {'a', 'b', 'c', 'd'}; // Use "^" to index from the end. var secondToLast = values.ElementAtOrDefault(^2); Console.WriteLine(secondToLast);

An important note. Conceptually, ElementAtOrDefault can make a collection be infinite. It can make every possible index returning a valid value—the default value.

And This could be useful if a collection is queried for invalid indexes, and actual stored values are not necessary for the algorithm.

These methods can transform how we access collections. ElementAtOrDefault eliminates the need for bounds-checking, but it can create extra complexity when handling the default value.