Lära Combining Collections | Sets and Collection Utilities

Combining collections is a common task in C#. Whether you are merging lists of items, uniting sets of unique values, or joining dictionaries based on shared keys, the .NET framework provides several methods to help. Three primary methods you will use are Concat, Union, and Join.

Concat: combines two sequences by appending one after the other, keeping all elements, including duplicates;
Union: combines two sequences and removes any duplicate elements, resulting in only unique items;
Join: connects elements from two collections based on a matching key, useful for combining dictionaries or lists of objects with shared properties.

Understanding these methods helps you choose the right approach for your data and ensures you do not lose or duplicate information unintentionally.

Program.cs


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using System;
using System.Collections.Generic;

namespace ConsoleApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            List<string> listA = new List<string> { "apple", "banana", "cherry" };
            List<string> listB = new List<string> { "banana", "date", "fig" };

            // Merge both lists
            List<string> merged = new List<string>();
            merged.AddRange(listA);
            merged.AddRange(listB);

            // Remove duplicates using a HashSet
            HashSet<string> uniqueSet = new HashSet<string>(merged);

            Console.WriteLine("Merged list with duplicates:");
            foreach (var item in merged)
            {
                Console.WriteLine(item);
            }

            Console.WriteLine("\nUnique items after removing duplicates:");
            foreach (var item in uniqueSet)
            {
                Console.WriteLine(item);
            }
        }
    }
}

When combining collections, you should think about your data and the outcome you want. If you simply append one list to another, you may end up with duplicate entries. Using a set, like HashSet<T>, ensures all values are unique after merging. This is especially useful for things like user IDs, product codes, or any case where duplicates would cause problems.

On the other hand, when working with dictionaries, joining them by key allows you to merge related data without losing information. However, you must be careful—if both dictionaries have the same key, you need to decide which value to keep or how to combine them. Sometimes, using Union with sets or careful joins with dictionaries is necessary to avoid accidental data loss or overwriting important information.

Program.cs


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

namespace ConsoleApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var dict1 = new Dictionary<int, string>
            {
                { 1, "Alice" },
                { 2, "Bob" },
                { 3, "Charlie" }
            };

            var dict2 = new Dictionary<int, string>
            {
                { 2, "Bobby" },
                { 3, "Charlotte" },
                { 4, "Diana" }
            };

            // Join dictionaries by key
            var joined = dict1.Join(
                dict2,
                d1 => d1.Key,
                d2 => d2.Key,
                (d1, d2) => new { Key = d1.Key, Value1 = d1.Value, Value2 = d2.Value }
            );

            Console.WriteLine("Joined dictionary entries by key:");
            foreach (var item in joined)
            {
                Console.WriteLine($"Key: {item.Key}, Value1: {item.Value1}, Value2: {item.Value2}");
            }
        }
    }
}

1. Which method combines two lists into one?

2. How can you remove duplicates when merging collections?

3. Fill in the blanks to join two dictionaries by key.

Var allt tydligt?

Tack för dina kommentarer!

Avsnitt 3. Kapitel 6

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Suggested prompts:

Can you show me code examples for merging lists, sets, and dictionaries in C#?

What are some common mistakes to avoid when combining collections?

How do I decide whether to use Concat, Union, or Join for my data?

Svep för att visa menyn

Concat: combines two sequences by appending one after the other, keeping all elements, including duplicates;
Union: combines two sequences and removes any duplicate elements, resulting in only unique items;
Join: connects elements from two collections based on a matching key, useful for combining dictionaries or lists of objects with shared properties.

Understanding these methods helps you choose the right approach for your data and ensures you do not lose or duplicate information unintentionally.

Program.cs


              1234567891011121314151617181920212223242526272829303132333435
            
using System;
using System.Collections.Generic;

namespace ConsoleApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            List<string> listA = new List<string> { "apple", "banana", "cherry" };
            List<string> listB = new List<string> { "banana", "date", "fig" };

            // Merge both lists
            List<string> merged = new List<string>();
            merged.AddRange(listA);
            merged.AddRange(listB);

            // Remove duplicates using a HashSet
            HashSet<string> uniqueSet = new HashSet<string>(merged);

            Console.WriteLine("Merged list with duplicates:");
            foreach (var item in merged)
            {
                Console.WriteLine(item);
            }

            Console.WriteLine("\nUnique items after removing duplicates:");
            foreach (var item in uniqueSet)
            {
                Console.WriteLine(item);
            }
        }
    }
}

Program.cs


              1234567891011121314151617181920212223242526272829303132333435363738394041
            
using System;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var dict1 = new Dictionary<int, string>
            {
                { 1, "Alice" },
                { 2, "Bob" },
                { 3, "Charlie" }
            };

            var dict2 = new Dictionary<int, string>
            {
                { 2, "Bobby" },
                { 3, "Charlotte" },
                { 4, "Diana" }
            };

            // Join dictionaries by key
            var joined = dict1.Join(
                dict2,
                d1 => d1.Key,
                d2 => d2.Key,
                (d1, d2) => new { Key = d1.Key, Value1 = d1.Value, Value2 = d2.Value }
            );

            Console.WriteLine("Joined dictionary entries by key:");
            foreach (var item in joined)
            {
                Console.WriteLine($"Key: {item.Key}, Value1: {item.Value1}, Value2: {item.Value2}");
            }
        }
    }
}

1. Which method combines two lists into one?

2. How can you remove duplicates when merging collections?

3. Fill in the blanks to join two dictionaries by key.

Var allt tydligt?

Tack för dina kommentarer!

Avsnitt 3. Kapitel 6