Conditionally update values in a List in C#

This post will discuss how to conditionally update values in a list in C#.

The Enumerable.Where() method filters a sequence of values based on a predicate. It is available in System.Linq namespace. The following code example demonstrates how we can use the Where() method with a foreach loop to conditionally update values in a list. The solution in-place updates the age of Robert from 20 to 18.

using System;

using System.Linq;

using System.Collections.Generic;

class Student

{

public string name { get; set; }

public decimal age { get; set; }

public override string ToString() {

return "[" + name + ", " + age + "]";

}

public class Example

{

public static void Main()

{

var list = new List<Student>

{

new Student{name = "Olivia", age = 10},

new Student{name = "Robert", age = 20},

new Student{name = "John", age = 15}

};

foreach (var item in list.Where(x => x.name == "Robert")) {

item.age = 18;

}

Console.WriteLine(String.Join(", ", list));

}

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Output:

[Olivia, 10], [Robert, 18], [John, 15]

The foreach loop can be replaced with the ForEach() method, as shown below:

using System;

using System.Linq;

using System.Collections.Generic;

class Student

{

public string name { get; set; }

public decimal age { get; set; }

public override string ToString() {

return "[" + name + ", " + age + "]";

}

public class Example

{

public static void Main()

{

var list = new List<Student>

{

new Student{name = "Olivia", age = 10},

new Student{name = "Robert", age = 20},

new Student{name = "John", age = 15}

};

list.Where(x => x.name == "Robert").ToList()

.ForEach(x => x.age = 18);

Console.WriteLine(String.Join(", ", list));

}

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Output:

[Olivia, 10], [Robert, 18], [John, 15]

Both above solutions in-place updates values in a list in C#. To leave the original list unchanged and return a new list with updated values, you can do like below:

using System;

using System.Linq;

using System.Collections.Generic;

class Student

{

public string name { get; set; }

public decimal age { get; set; }

public override string ToString() {

return "[" + name + ", " + age + "]";

}

public class Example

{

public static void Main()

{

var list = new List<Student>

{

new Student{name = "Olivia", age = 10},

new Student{name = "Robert", age = 20},

new Student{name = "John", age = 15}

};

var result = list.Where(x => x.name == "Robert")

.Select(x => { x.age = 18; return x; });

Console.WriteLine(String.Join(", ", result));

}

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Output:

[Robert, 18]

That’s all about conditionally updating values in a list in C#.

Conditionally update values in a List in C#

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