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Change big collection into unique List of collections

I have a big list of objects and in this object there is a category ID something like:
var list = new List<Example>
{
new Example {CatId = 1, Value = new { }},
new Example {CatId = 1, Value = new { }},
new Example {CatId = 1, Value = new { }},
new Example {CatId = 2, Value = new { }},
new Example {CatId = 2, Value = new { }},
new Example {CatId = 3, Value = new { }}
// and so on
};
So I am looking for making this complicated list more organized like list of lists of unique elements
something like:
var result = new List<List<Example>>
{
new List<Example>
{
new Example {CatId = 1, Value = new { }},
new Example {CatId = 2, Value = new { }},
new Example {CatId = 3, Value = new { }}
},
new List<Example>
{
new Example {CatId = 1, Value = new { }},
new Example {CatId = 2, Value = new { }}
},
new List<Example>
{
new Example {CatId = 1, Value = new { }}
}
}
Problem is I do not what to use, group by will not fix my case, so how to do this in most efficient way.

So this is about partitioning, it's the sort of thing that is easy to do in a database query, but in c# you need to create some key with a partition number that you can then use to .GroupBy.
The partitioning itself is a grouping
var projected = list.GroupBy(x => x.CatId)
.SelectMany( g => g.Select( ( x, i ) => new { Item = x, rn = i + 1 } ) );
This gives you records that look like:
{"Item":{"CatId":1,"Value":{}},"rn":1}
{"Item":{"CatId":1,"Value":{}},"rn":2}
{"Item":{"CatId":1,"Value":{}},"rn":3}
{"Item":{"CatId":2,"Value":{}},"rn":1}
{"Item":{"CatId":2,"Value":{}},"rn":2}
{"Item":{"CatId":3,"Value":{}},"rn":1}
As you can see that rn ("row number") value can be used to group by:
var result = projected.GroupBy(x => x.rn, x => x.Item);
This gives us:
[{"CatId":1,"Value":{}},{"CatId":2,"Value":{}},{"CatId":3,"Value":{}}]
[{"CatId":1,"Value":{}},{"CatId":2,"Value":{}}]
[{"CatId":1,"Value":{}}]
So, all in 1 go:
var result = list.GroupBy(x => x.CatId)
.SelectMany( g => g.Select( ( x, i ) => new { Item = x, rn = i + 1 } ) )
.GroupBy(x => x.rn, x => x.Item);
Live example: https://dotnetfiddle.net/AlTfk8

Cartesian Product of an arbitrary number of objects [duplicate]

This question already has answers here:
Is there a good LINQ way to do a cartesian product?
(3 answers)
Closed 4 years ago.
I'm looking to get the Cartesian Product of an arbitrary number of objects in c#. My situation is slightly unusual - my inputs are not lists of base types, but objects which have a property that's a list of base types.
My input and output objects are as follows:
public class Input
{
public string Label;
public List<int> Ids;
}
public class Result
{
public string Label;
public int Id;
}
Some sample input data:
var inputs = new List<Input>
{
new Input { Label = "List1", Ids = new List<int>{ 1, 2 } },
new Input { Label = "List2", Ids = new List<int>{ 2, 3 } },
new Input { Label = "List3", Ids = new List<int>{ 4 } }
};
And my expected output object:
var expectedResult = new List<List<Result>>
{
new List<Result>
{
new Result{Label = "List1", Id = 1},
new Result{Label = "List2", Id = 2},
new Result{Label = "List3", Id = 4}
},
new List<Result>
{
new Result{Label = "List1", Id = 1},
new Result{Label = "List2", Id = 3},
new Result{Label = "List3", Id = 4}
},
new List<Result>
{
new Result{Label = "List1", Id = 2},
new Result{Label = "List2", Id = 2},
new Result{Label = "List3", Id = 4}
},
new List<Result>
{
new Result{Label = "List1", Id = 2},
new Result{Label = "List2", Id = 3},
new Result{Label = "List3", Id = 4}
}
};
If I knew the number of items in 'inputs' in advance I could do this:
var knownInputResult =
from id1 in inputs[0].Ids
from id2 in inputs[1].Ids
from id3 in inputs[2].Ids
select
new List<Result>
{
new Result { Id = id1, Label = inputs[0].Label },
new Result { Id = id2, Label = inputs[1].Label },
new Result { Id = id3, Label = inputs[2].Label },
};
I'm struggling to adapt this to an arbitrary number of inputs - is there a possible way to do this?

I consider this duplicate of question linked in comments, but since it was reopened and you struggle to adapt that question to your case, here is how.
First grab function by Eric Lippert from duplicate question as is (how it works is explained there):
public static class Extensions {
public static IEnumerable<IEnumerable<T>> CartesianProduct<T>(this IEnumerable<IEnumerable<T>> sequences)
{
IEnumerable<IEnumerable<T>> emptyProduct = new[] { Enumerable.Empty<T>() };
return sequences.Aggregate(
emptyProduct,
(accumulator, sequence) =>
from accseq in accumulator
from item in sequence
select accseq.Concat(new[] { item })
);
}
}
Then flatten your input. Basically just attach corresponding label to each id:
var flatten = inputs.Select(c => c.Ids.Select(r => new Result {Label = c.Label, Id = r}));
Then run cartesian product and done:
// your expected result
var result = flatten.CartesianProduct().Select(r => r.ToList()).ToList();

I'm not proud of the amount of time I spent messing with this, but it works.
It's basically black magic, and I would replace it the first chance you get.
public static List<List<Result>> Permutate(IEnumerable<Input> inputs)
{
List<List<Result>> results = new List<List<Result>>();
var size = inputs.Select(inp => factorial_WhileLoop(inp.Ids.Count)).Aggregate((item, carry) => item + carry) - 1;
for (int i = 0; i < size; i++) results.Add(new List<Result>());
foreach (var input in inputs)
{
for (int j = 0; j < input.Ids.Count; j++)
{
for (int i = 0; i < (size / input.Ids.Count); i++)
{
var x = new Result() { Label = input.Label, Id = input.Ids[j] };
results[(input.Ids.Count * i) + j].Add(x);
}
}
}
return results;
}
public static int factorial_WhileLoop(int number)
{
var result = 1;
while (number != 1)
{
result = result * number;
number = number - 1;
}
return result;
}

Join collections by id with linq [duplicate]

This question already has answers here:
Join/Where with LINQ and Lambda
(10 answers)
Closed 5 years ago.
I have a object collection
var myData = new[]
{
new {
ID = "1285",
COUNT = 45
},
new {
ID = "1286",
COUNT = 156
},
new {
ID = "1287",
COUNT = 965
}
};
And my another collection comes from another data source like this:
var incomingData = new[]
{
new {
ID = "1285",
LOCATION = "City-1"
},
new {
ID = "1286",
LOCATION = "City-2"
},
new {
ID = "1287",
LOCATION = "City-3"
}
};
I want to change incoming data with COUNT property by Id.
var NewData = new[]
{
new {
ID = "1285",
LOCATION = "City-1",
COUNT = 45
},
new {
ID = "1286",
LOCATION = "City-2",
COUNT = 156
},
new {
ID = "1287",
LOCATION = "City-3",
COUNT = 965
}
};
How can I do this with linq labda functions. I do not want to use foreach loop. (myData and incomingData collection lengths may be different)

Just use ordinary join statements like this:
var result=
(
from data in myData
join inData in incomingData
on data.ID equals inData.ID
select new
{
data.ID,
inData.LOCATION,
data.COUNT
}
).ToList();
Easy, simple, readable

how to write linq expression to filter navigational property based on status?

parent category contains a list of sub categories and sub categories contains a list of sub categories. Now I want to fetch all parent categories if its status is true along with subcategories. I want to check the subcategories status also while fetching. My current query is
db.Categories.Where(x => x.Status)
.Include(x=>x.SubCategories)
. OfType<ParentCategory>().ToList();
how to check the status of subcategories in this query??

Try LINQ's SelectMany() method. It is used to flatten nested collections. Instead of using nested for loops, we can do the task in a more 'LINQ' way.
Ex given below -
Master m1 = new Master() { name = "A", lstObj = new List<obj> { new obj { i = 1, s = "C++" }, new obj { i = 1, s = "C#" }, new obj { i = 1, s = "Java" } } };
Master m2 = new Master() { name = "A", lstObj = new List<obj> { new obj { i = 4, s = "PHP" }, new obj { i = 5, s = "Ruby" }, new obj { i = 6, s = "Perl" } } };
List<Master> lstMasters = new List<Master> { m1, m2 };
var result = lstMasters.SelectMany(m => m.lstObj).Where(o => o.s == "PHP");
Just replace the Master class with your own master class.

Select top N records after filtering in each group

I am an old bee in .NET but very new to Linq! After some basic reading I have decided to check my skill and I failed completely! I don't know where I am making mistake.
I want to select highest 2 order for each person for while Amount % 100 == 0.
Here is my code.
var crecords = new[] {
new {
Name = "XYZ",
Orders = new[]
{
new { OrderId = 1, Amount = 340 },
new { OrderId = 2, Amount = 100 },
new { OrderId = 3, Amount = 200 }
}
},
new {
Name = "ABC",
Orders = new[]
{
new { OrderId = 11, Amount = 900 },
new { OrderId = 12, Amount = 800 },
new { OrderId = 13, Amount = 700 }
}
}
};
var result = crecords
.OrderBy(record => record.Name)
.ForEach
(
person => person.Orders
.Where(order => order.Amount % 100 == 0)
.OrderByDescending(t => t.Amount)
.Take(2)
);
foreach (var record in result)
{
Console.WriteLine(record.Name);
foreach (var order in record.Orders)
{
Console.WriteLine("-->" + order.Amount.ToString());
}
}
Can anyone focus and tell me what would be correct query?
Thanks in advance

Try this query:
var result = crecords.Select(person =>
new
{
Name = person.Name,
Orders = person.Orders.Where(order => order.Amount%100 == 0)
.OrderByDescending(x => x.Amount)
.Take(2)
});
Using your foreach loop to print the resulting IEnumerable, the output of it is:
XYZ
-->200
-->100
ABC
-->900
-->800

This has already been answered but if you didn't want to create new objects and simply modify your existing crecords, the code would look like this alternatively. But you wouldn't be able to use anonymous structures like shown in your example. Meaning you would have to create People and Order classes
private class People
{
public string Name;
public IEnumerable<Order> Orders;
}
private class Order
{
public int OrderId;
public int Amount;
}
public void PrintPeople()
{
IEnumerable<People> crecords = new[] {
new People{
Name = "XYZ",
Orders = new Order[]
{
new Order{ OrderId = 1, Amount = 340 },
new Order{ OrderId = 2, Amount = 100 },
new Order{ OrderId = 3, Amount = 200 }
}
},
new People{
Name = "ABC",
Orders = new Order[]
{
new Order{ OrderId = 11, Amount = 900 },
new Order{ OrderId = 12, Amount = 800 },
new Order{ OrderId = 13, Amount = 700 }
}
}
};
crecords = crecords.OrderBy(record => record.Name);
crecords.ToList().ForEach(
person =>
{
person.Orders = person.Orders
.Where(order => order.Amount%100 == 0)
.OrderByDescending(t => t.Amount)
.Take(2);
}
);
foreach (People record in crecords)
{
Console.WriteLine(record.Name);
foreach (var order in record.Orders)
{
Console.WriteLine("-->" + order.Amount.ToString());
}
}
}