I have a requirement to select top N elements of related products from a big list of products.
So far, I have below code and it works perfectly.
class Product
{
public string Name;
public double Rating;
public List<Product> RelatedProducts;
public List<Product> GetTopRelatedProducts(int N)
{
var relatedSet = new HashSet<Product>();
var relatedListQueue = new Queue<List<Product>>();
if (RelatedProducts != null && RelatedProducts.Count > 0)
relatedListQueue.Enqueue(RelatedProducts);
while (relatedListQueue.Count > 0)
{
var relatedList = relatedListQueue.Dequeue();
foreach (var product in relatedList)
{
if (product != this && relatedSet.Add(product) && product.RelatedProducts != null && product.RelatedProducts.Count > 0)
relatedListQueue.Enqueue(product.RelatedProducts);
}
}
return relatedSet.OrderByDescending(x => x.Rating).Take(N).OrderBy(/*How to order by occurrence here? */).ToList();
}
}
Now, I want GetTopRelatedProducts method to remember the occurrence order of top N products. First added product to the HashSet will be at the begining of the returned List.
For example, if I have this scenario:
//...
relatedSet.Add(new Product(){Name="A", Rating=3});
relatedSet.Add(new Product(){Name="B", Rating=4});
relatedSet.Add(new Product(){Name="C", Rating=5});
//...
and if N = 2, the method should return : B,C instead of C,B because B was added first to the HashSet.
So I changed the return statement in the method to:
var relatedSetCopy = relatedSet.ToList();
return (from p in relatedSet.OrderByDescending(x => x.Rate).Take(N)
join c in relatedSetCopy on p.Name equals c.Name
let index = relatedSetCopy.IndexOf(c)
orderby index
select p).ToList();
Basically, I use LINQ Join to re-order the list in the same way it was before the ordering on Rating.
I want to do it this way because first added product has more similarity with selected product than others.
I have two questions here:
Is there a better way to re-order the returned list?
Is there a better design to handle relation between products? (I was thinking about implementing a tree structure. So object navigation and retrieval will be faster)
Is there a better way to re-order the returned list?
You can simply Intersect the relatedSet with the top N related reordered set because Intersect yields the items based on their order in the first sequence.
So instead of
return relatedSet.OrderByDescending(x => x.Rating).Take(N).ToList();
you would use
return relatedSet.Intersect(relatedSet.OrderByDescending(x => x.Rating).Take(N)).ToList();
Related
I have a list of Ids and I want to fetch those records from my Products table (present in database) where Product Id matches to any Ids given in the following list.
List<int> ids = new List<int> { 1, 2, 3 };
I know I can do like this ->
_unitOfWork.Product.GetAll(p => p.Id == 1 || p.Id == 2 || p.Id == 3);
But problem with this is my list is dynamic. Here just for example I hard coded 3 values but it could be the list of n numbers. So in that case it will fail.
So, I want to know if there a way to or condition like ->
_unitOfWork.Product.GetAll(p => p.Id == //all ids present in list with OR conditions, something like foreach loop which will iterate through my list of ids & internally will make condition like I made above with hard coded values);
I am using repository pattern in my project, hence my GetAll() method looks like this:
public IEnumerable<T> GetAll(Expression<Func<T, bool>>? filter = null, string? includeProperties = null)
{
IQueryable<T> query = dbSet;
if (filter != null)
{
query = query.Where(filter);
}
if (includeProperties != null)
{
query = IncludeProperties(query,includeProperties);
}
return query.ToList();
}
You can use .Any(),
List<int> ids = new List<int> { 1, 2, 3 };
_unitOfWork.Product.GetAll(p => ids.Any(x => x == p.Id));
Alternate way you can also use .Contains()
_unitOfWork.Product.GetAll(p => ids.Contains(p.Id));
We're new in LINQ and we want to know if the are any method to check if there are elements remaining in the sentence like the ResultSet.next() from Java.
In Java the resultSet return true if there are elements remaining and false if not. We want to know if the is a method like that in LINQ.
public List<Product> FindProductsByKeyword(string productName, Category category, int page, int size)
{
DbSet<Product> products = Context.Set<Product>();
List<Product> result;
if (category == null)
{
result = (from p in products
where p.productName.Contains(productName) //, StringComparison.OrdinalIgnoreCase)
orderby p.productName descending
select p).Skip(page).Take(size).Include("Category").ToList();
}
else
{
result = (from p in products
where p.productName.Contains(productName)
&& p.categoryId == category.id
orderby p.productName descending
select p).Skip(page).Take(size).ToList();
}
return result;
}
This our code( I dont know if this will help) we take elements with a number of Size but we dont know if there are more elements.
Using the terminating method ToList() initiates a DB query and parses the returned table as a simple in-memory List<T> (same as ArrayList<T> in Java).
If you want to check if there are any entries in the result, you can just check the list's Count property:
if (result.Count > 0)
{
// Do something
}
Or use LINQ's Any() extension method, which is a bit more readable in this context:
if (result.Any())
{
// Do something
}
If you returned an Enumerable, then you could use Enumerable.MoveNext()
For example:
var p = products.AsEnumerable();
var i = p.GetEnumerator();
while( i.MoveNext())
i.Current.productfieldname.Dump() // LinqPad .Dump() shows value
I have used two IList object. In first list, it contains 10 records and the second contains 5 records. Now I want to update the first IList with second IList data.
foreach (ObjList newlist in New)
{
ObjList list = ExtList.FirstOrDefault(x => x.Id == newlist.Id);
if (list!= null)
{
ExtList.Remove(list);
ExtList.Add(newlist);
}
}
I tried the above. But the added object appended at the end of the list. So sort order changed. I need it in the same existing order.
Updated
I tried the sorting, but it is not sorted.
ExtList.OrderBy(x => x.Id);
You can try using IList.Insert() to add new item at the index of to-be-replaced item, so that you can keep the list in it's original order :
ObjList list = ExtList.FirstOrDefault(x => x.Id == newlist.Id);
if (list!= null)
{
var position = ExtList.IndexOf(list);
ExtList.Insert(position, newlist);
ExtList.Remove(list);
}
If you want to keep the order after update, you can :
ExtList=(from e in ExtList
join n in New
on e.Id equals n.Id into left
from n in left.DefaultIfEmpty()
select new /*Class Name */
{
Id=e.Id,
Name=n==null?e.Name:n.Name
}).ToList();
You should use ExtList.IndexOf instead ExtList.FirstOrDefault.
And then use ExtList.Insert to given index instead ExtList.Add
I have 2 lists. 1 is a collection of products. And the other is a collection of products in a shop.
I need to be able to return all shopProducts if the names match any Names in the products.
I have this but it doesn't seem to work. Any ideas?
var products = shopProducts.Where(p => p.Name.Any(listOfProducts.
Select(l => l.Name).ToList())).ToList();
I need to say give me all the shopproducts where name exists in the other list.
var products = shopProducts.Where(p => listOfProducts.Any(l => p.Name == l.Name))
.ToList();
For LINQ-to-Objects, if listOfProducts contains many items then you might get better performance if you create a HashSet<T> containing all the required names and then use that in your query. HashSet<T> has O(1) lookup performance compared to O(n) for an arbitrary IEnumerable<T>.
var names = new HashSet<string>(listOfProducts.Select(p => p.Name));
var products = shopProducts.Where(p => names.Contains(p.Name))
.ToList();
For LINQ-to-SQL, I would expect (hope?) that the provider could optimise the generated SQL automatically without needing any manual tweaking of the query.
You could use a join, for example:
var q = from sp in shopProducts
join p in listOfProducts on sp.Name equals p.Name
select sp;
A fuller guide on join is here.
You could create an IEqualityComparer<T> that says products with equal names are equal.
class ProductNameEqulity : IEqualityComparer<Product>
{
public bool Equals(Product p1, Product p2)
{
return p1.Name == p2.Name
}
public int GetHashCode(Product product)
{
return product.Name.GetHashCode();
}
}
Then you can use this in the Intersect extension method.
var products = shopProducts.Intersect(listOfProducts, new ProductNameEquality());
Try this please
var products = shopProducts.Where(m=> listOfProducts.Select(l=>l.Name).ToList().Contains(m=>m.Name));
var products = shopProducts
.Where(shopProduct =>
listOfProducts.Any(p => shopProduct.Name == p.Name))
.ToList();
I have a list with two or more objects of class Agent.
Name = "A"
Priority = 0
ResultCount = 100
;
Name = "B"
Priority = 1
ResultCount = 100
;
Both objects have the same ResultCount. In that case I only need one object and not two or more. I did this with a Linq Query with Distinct and an custom made Comparer.
IEnumerable<Agent> distinctResultsAgents =
(from agt in distinctUrlsAgents select agt).Distinct(comparerResultsCount);
With this query I get only one object from the list but I never know which one.
But I don't want just any object, I want object "B" because the Priority is higher then object "A".
How can I do that?
My custom Comparer is very simple and has a method like this:
public bool Equals(Agent x, Agent y)
{
if (x == null || y == null)
return false;
if (x.ResultCount == y.ResultCount)
return true;
return false;
}
First group the elements by ResultCount so that you only get one result for each distinct value of ResultCount. Then for each group select the element in that group with the highest priority.
Try this query:
IEnumerable<Agent> distinctResultsAgents =
from d in distinctUrlsAgents
group d by d.ResultCount into g
select g.OrderByDescending(x => x.Priority).First();
If you use morelinq there is a function called MaxBy that you could use instead of the last line, but note that it only works for LINQ To Objects.