how to group by name having different Ids in linq - linq

Question

I am trying to understand the group by keyword and I made sample data sets.
If I want to group by name, then I lose product ID. So I couldn't complete the issues.
Data Structure
Product=[
{id: 1, name:"desktop", productCategoryId:1},
{id: 2, name:"laptop", productCategoryId:1},
{id: 3, name:"desktop", productCategoryId:1},
{id: 4, name:"laptop", productCategoryId:1},
{id: 5, name:"desktop", productCategoryId:1},
];
ProductCategory =[
{productCategoryId: 1, name:"desktop"},
{productCategoryId: 2, name:"Electronics"},
{productCategoryId: 3, name:"Furniture"},
];
If you want to group by Product Name and want to get the result as below, what linq query can I use?
Result I want
Result = [
{
id: 1, name: "desktop", productCategoryId:1,
},
{
id: 2, name: "laptop", productCategoryId:1,
},
]

Answer 1

Your requirement has some shortcomings. I don't know why you would use Product1 in your end result and not Product[3]. Furthermore: all Products have ProductCategory 1. What if some of them have ProductCategory [2]?
So all I can tell you how to use GroupBy.
If you have a sequence of similar items, and you want to group these items into groups that have something in common, you can use one of the overloads of [Enumerable.GroupBby].1.
You'll have to say what the items in one group have in common. This is done using parameter KeySelector. It has the following format:
IEnumerable<Product> products = ...
var productsWithSameName = product.GroupBy(
// KeySelector: make groups of Products with the same Name:
product => product.Name,
...
);
The part product => product.Name is the keySelector. It means: from every element of your input sequence, take property Name.
By the way: to make it easier to read, convention is to use plural nouns to identify collections, and use singular nouns to identify elements of the collection. So the collection is a collection of Products, one element of the collection is identified by parameter product.
So, from every product in the collection of Products, we take the value of property Name. We put all Products with the same Name into groups. Every group will have a Key, which is the value of the item that all elements in the group have in common.
In our case, all elements of the group with Key == "laptop" will have a value of property Name equal to "laptop".
On the left side of the => is one Product, on the right side of the => is the object that we will use to group the items on. This can be a simple property value, but it can also be composed from several properties:
If you want to make groups of families that live in the same country with the same number of children, your keySelector will be:
family => family => new
{
Country = family.Country
ChildrenCount = family.Childrend.Count(),
},
This will give you the following groups:
USA families without Children
USA families with one Child
USA families with two Children
Indian families without Children
Indian families with one Child
Dutch families without Children
etc.
You will not have groups without elements: every group will have at least one element. All elements in the group will have the same value for Key. The group is identified by this Key. Every group will have a unique key, otherwise these groups should have been combined in one group.
If you use the overload of GroupBy that has only a keySelector, you will make groups of Products that have the same key:
IEnumerable<Product> products = ...
var groupsOfProductsWithSameName = products.GroupBy(product => product.Name);
foreach (var group in groupsOfProductsWithSameName
{
string commonName = group.Key;
IEnumerable<Product> productsWithThisName = group;
foreach (product in productsWithThisName)
{
Assert(product.Name == group.Key);
}
}
So every group will have a Key, which is the result of the keySelector. Every element of the group will be a product that has a Name equal to the Key of the group.
Nota Bene: the group IS a sequence, not HAS a sequence!
One of the overloads of GroupBy has an extra parameter: resultSelector. It takes the form:
(key, productsWithThisKey) => ...
This means: from every key that we found, and all productsWithThisKey, do the following ...
So for instance: we make groups of products with the same name, and from every group we want to remember the name, the number of products in the group and the lowest 10 Ids of the products in the group as the first page of products.
IEnumerable<Product> products = ...
var firstProductPage = products.GroupBy(
// parameter keySelector: make groups with same Name
product => product.Name,
// parameter resultSelector:
// for every Name that we found, and all products with this name, make one new:
(name, productsWithThisName) => new
{
Name = name,
NumberOfProducts = productsWithThisName.Count(),
Ids = productsWithThisName.Select(product => product.Id)
.Take(10)
.ToList(),
});
With parameter resultSelector you can define exactly what should be in each Group.