How can we update the values of a collection using LINQ in C#?

LINQ provides several approaches to update collection values in C#. While LINQ is primarily designed for querying data, you can combine it with other methods to modify collection elements efficiently.

Using ForEach with List Collections

The List<T> class provides a ForEach method that can be used to update all elements in the collection −

using System;
using System.Collections.Generic;

namespace DemoApplication {
    class Program {
        static void Main(string[] args) {
            List<Fruit> fruits = new List<Fruit> {
                new Fruit {
                    Name = "Apple",
                    Size = "Small"
                },
                new Fruit {
                    Name = "Orange",
                    Size = "Small"
                }
            };
            
            foreach(var fruit in fruits) {
                Console.WriteLine($"Fruit Details Before Update. {fruit.Name}, {fruit.Size}");
            }
            
            fruits.ForEach(fruit => { fruit.Size = "Large"; });
            
            foreach (var fruit in fruits) {
                Console.WriteLine($"Fruit Details After Update. {fruit.Name}, {fruit.Size}");
            }
        }
    }
    
    public class Fruit {
        public string Name { get; set; }
        public string Size { get; set; }
    }
}

The output of the above code is −

Fruit Details Before Update. Apple, Small
Fruit Details Before Update. Orange, Small
Fruit Details After Update. Apple, Large
Fruit Details After Update. Orange, Large

Using Where() for Conditional Updates

To update collection items based on specific conditions, combine Where() with a foreach loop −

using System;
using System.Collections.Generic;
using System.Linq;

namespace DemoApplication {
    class Program {
        static void Main(string[] args) {
            List<Fruit> fruits = new List<Fruit> {
                new Fruit {
                    Name = "Apple",
                    Size = "Small"
                },
                new Fruit {
                    Name = "Orange",
                    Size = "Small"
                },
                new Fruit {
                    Name = "Mango",
                    Size = "Medium"
                }
            };
            
            foreach(var fruit in fruits) {
                Console.WriteLine($"Fruit Details Before Update. {fruit.Name}, {fruit.Size}");
            }
            
            foreach (var fruit in fruits.Where(w => w.Size == "Small")) {
                fruit.Size = "Large";
            }
            
            foreach (var fruit in fruits) {
                Console.WriteLine($"Fruit Details After Update. {fruit.Name}, {fruit.Size}");
            }
        }
    }
    
    public class Fruit {
        public string Name { get; set; }
        public string Size { get; set; }
    }
}

The output of the above code is −

Fruit Details Before Update. Apple, Small
Fruit Details Before Update. Orange, Small
Fruit Details Before Update. Mango, Medium
Fruit Details After Update. Apple, Large
Fruit Details After Update. Orange, Large
Fruit Details After Update. Mango, Medium

Using Select() to Create Updated Collections

For immutable updates, use Select() to create a new collection with updated values −

using System;
using System.Collections.Generic;
using System.Linq;

namespace DemoApplication {
    class Program {
        static void Main(string[] args) {
            List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };
            
            Console.WriteLine("Original numbers:");
            foreach (var num in numbers) {
                Console.Write(num + " ");
            }
            Console.WriteLine();
            
            var updatedNumbers = numbers.Select(x => x * 2).ToList();
            
            Console.WriteLine("Updated numbers (doubled):");
            foreach (var num in updatedNumbers) {
                Console.Write(num + " ");
            }
            Console.WriteLine();
        }
    }
}

The output of the above code is −

Original numbers:
1 2 3 4 5 
Updated numbers (doubled):
2 4 6 8 10 

Comparison of Update Methods

Conclusion

LINQ can be effectively combined with traditional loops to update collection values. Use ForEach() for bulk updates, Where() with loops for conditional updates, and Select() when you need to create new collections with transformed data while preserving the original.