Rearrange a C# list of objects when one property has duplicates

Question

0.00/5 (No votes)

See more:

I have a list in C# defined like this:

public class Author  
{  
    public string Name { get; set; }  
    public string Book { get; set; }
    public string Age { get; set; }
    public string Address { get; set; }
    
} 

List<Author> originalAuthorList = new List<Author>
{
    new Author{ Name = "Bob", Age = "30", Address = "123 Main St.", Book = "Bob's First Book", },
    new Author{ Name = "Dan", Age = "32", Address = "456 main St.", Book = "Dan's First Book" },
    new Author{ Name = "Dan", Age = "32", Address = "456 main St.", Book = "Dan's Second Book" },
    new Author{ Name = "Tom", Age = "34", Address = "789 main St.", Book = "Tom's First Book" }
};

How could I rearrange the list to look like this:

List<Author> newAuthorList = new List<Author>
{
    new Author{ Name = "Bob", Age = "30",  Address = "123 Main St.", Book = "Bob's First Book" },
    new Author{ Name = "Dan", Age = "32",  Address = "456 Main St.", Book = "Dan's First Book, Dan's Second Book" },
    new Author{ Name = "Tom", Age = "34",  Address = "789 Main St.", Book = "Tom's First Book" }
};

What I have tried:

I know that if I only had 2 fields, for example, Name and Book, I could do this:

List<Author> newAuthorList = originalAuthorList
    .GroupBy(
        a => a.Name, // Group by name
        a => a.Book) // Select the book as the element
    .Select(g => new Author
    {
        Name = g.Key,
        Book = string.Join(", ", g) // Join the books together
    })
    .ToList();

But, how would I include all 4 fields in the new list?

Posted 23-Sep-20 5:17am

Jeffrey Taylor

Updated 23-Sep-20 22:09pm

Add a Solution

Comments

BillWoodruff 23-Sep-20 16:48pm

if you have control over the structure of the Author Class, and the data format used to create instances of that Class: if you can change 'Books from string to List<string> :

I'll share some code with you ... on your request

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

George Swan · Answer 1 · 2020-09-23T22:09:00

Solution 2

If you are familiar with Linq, you can do something like this

C#

var authors = originalAuthorList.
GroupBy(a => (a.Name, a.Age, a.Address), a => a.Book);
foreach (var grp in authors)
  {
   Console.WriteLine($"Name={grp.Key.Name}, Age={grp.Key.Age}, Address={grp.Key.Address} Books {string.Join(", ", grp)}");
  }

Posted 23-Sep-20 22:09pm

George Swan

Comments

BillWoodruff 24-Sep-20 15:35pm

+5 I learned something from your use of String.Join in the code ! That is an advanced example.

Might as well convert to Dictionary ?

var dict = authors.ToDictionary(
grp => grp.Key, grp => string.Join(", ", grp)
);

thanks, Bill

George Swan 24-Sep-20 16:56pm

Thanks Bill. Using a Dictionary is probably the most efficient solution. I find that there are usually faster solutions than Linq provides but they are not as much fun to write. Regards, George.

OriginalGriff · Answer 2 · 2020-09-23T05:57:00

Start here: Using Linq to create a Dictionary of sub-Lists by grouping from a collection.[^]
That lets you create a Dictionary which has the author name as the Key, and a List of all his Author entries as a Value.
You can then run through each group and use String.Join[^] to change the books to a comma list under a new Author entry.