Select objects with unique ID's as another object type using LINQ

Question

Using LINQ, I'm trying to select unique Customer's as Person objects. I'm using JSON data in the following example but I'm working with POCO objects in C#. In this example, I chose JSON to keep things simple.

I have the following Customer list:

[
  {
     "id": 123,
     "name: "John Smith",
     "transactionDate": "2019-08-21T10:30",
     "amount": 8.50
  },
  {
     "id": 234,
     "name: "Jane Doe",
     "transactionDate": "2019-08-22T18:21",
     "amount": 75.00
  },
  {
     "id": 123,
     "name: "John Smith",
     "transactionDate": "2019-08-26T10:30",
     "amount": 10.00
  }
]

I want to get the unique customers as Person objects and the result, should look like this:

[
  {
     "id": 123,
     "name": "John Smith"
  },
  {
     "id": 234,
     "name": "Jane Doe"
  }
]

The following should give me the unique ID's.

var uniqueIds = customers.Select(x => x.id).Distinct();

How do I now extract unique Person's from List<Customer>()?

Possible duplicate of [LINQ's Distinct() on a particular property](https://stackoverflow.com/questions/489258/linqs-distinct-on-a-particular-property) — aloisdg, Aug 27 '19 at 06:39
What if you have two objects with id 123, one named "John Smith", the other "Smith, John"? — Lasse V. Karlsen, Aug 27 '19 at 06:43
Please avoid editing the question with a solution. Instead, add the solution as an answer. — Zohar Peled, Aug 27 '19 at 17:47

score 1 · Answer 1 · answered Aug 27 '19 at 06:39

1

One way is to use GroupBy:

var uniquePersons = customers
    .GroupBy(c => new Person() {Id = c.Id, Name = c.Name})
    .Select(g => g.Key)
    .ToList();

answered Aug 27 '19 at 06:39

Zohar Peled

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This is a duplicate: https://stackoverflow.com/questions/489258/linqs-distinct-on-a-particular-property – aloisdg Aug 27 '19 at 06:40
@aloisdg I'm not sure it's an exact duplicate, but yes, the answers to the question you suggested can probably help the OP to solve their problem. – Zohar Peled Aug 27 '19 at 06:42
This got me close but didn't work. I updated the original post that shows what worked. – Sam Aug 27 '19 at 17:05

score 1 · Accepted Answer · answered Aug 27 '19 at 17:59

The suggested answer or the other SO post didn't return the results I needed. Here's the code that worked.

var uniquePersons = customers
                        .Select(x => new Person() { Id = x.Id, Name = x.Name })
                        .GroupBy(g => g.Id)
                        .Select(x => x.First())
                        .ToList();

I'm not saying this is the best way but this is what gave me a unique list of Person from a list of Customer.

I'd love to hear suggestions or explanations whether this is the best way to handle it or why the suggested answer didn't produce a List<Person>() with unique persons.

Select objects with unique ID's as another object type using LINQ

2 Answers2