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C# select duplicate using group

I would like to select only from non-blank Names where any Group contains same ID multiple times:
Data Setup
var a1 = new { id = 3, Name = "", Group = "GroupA" };
var a2 = new { id = 2, Name = "", Group = "GroupA" };
var a3 = new { id = 3, Name = "", Group = "GroupA" };
var b1 = new { id = 4, Name = "B", Group = "GroupB" };
var b2 = new { id = 5, Name = "B", Group = "GroupB" };
var b3 = new { id = 5, Name = "B", Group = "GroupB" };
List<dynamic> group = new List<dynamic>();
group.Add(a1);
group.Add(a2);
group.Add(a3);
group.Add(b1);
group.Add(b2);
group.Add(b3);
Query:
var query1 = group.ToList()
.Where(s=>s.Name != "")
.GroupBy(x =>x.Group)
.Where(g => g.Count() > 1)
.SelectMany(y => y)
.ToList();
Console.WriteLine("output\n" + string.Join("\n", query1));
Returns
id = 4, Name = B, Group = GroupB
id = 5, Name = B, Group = GroupB
id = 5, Name = B, Group = GroupB
But what I wanted is the following:
id = 5, Name = B, Group = GroupB
id = 5, Name = B, Group = GroupB
What am I doing wrong?

Group by id and/or Name depending on your needs
.GroupBy(x => new {x.id, x.Name})
Given
var list = new[]
{
new {id = 3, Name = "", Group = "GroupA"},
new {id = 2, Name = "", Group = "GroupA"},
new {id = 3, Name = "", Group = "GroupA"},
new {id = 4, Name = "B", Group = "GroupB"},
new {id = 5, Name = "B", Group = "GroupB"},
new {id = 5, Name = "B", Group = "GroupB"}
};
Usage
var results = list
.Where(s => s.Name != "")
.GroupBy(x => new {x.id, x.Name})
// .GroupBy(x => x.id) <- depending on your needs
.Where(g => g.Count() > 1)
.SelectMany(y => y);
foreach (var result in results)
Console.WriteLine($"{result.id}, {result.Name}, {result.Group}");
Output
5, B, GroupB
5, B, GroupB

You are applying GroupBy to Group property. Instead of Grouping by Group property, use id property,
Input
var list = new[]
{
new {id = 3, Name = "", Group = "GroupA"},
new {id = 2, Name = "", Group = "GroupA"},
new {id = 3, Name = "", Group = "GroupA"},
new {id = 4, Name = "B", Group = "GroupB"},
new {id = 5, Name = "B", Group = "GroupB"},
new {id = 5, Name = "B", Group = "GroupB"}
};
Solution:
var query1 = list.ToList()
.Where(s=>s.Name != "")
.GroupBy(x =>x.id)
//^^^^^ This change you need to do
.Where(g => g.Count() > 1)
.SelectMany(y => y)
.ToList();
Output
5, B, GroupB
5, B, GroupB
Try it online

Data Set to Tree Structure

I have the below set of data
Where each City belongs to a specific Department, which belongs to a specific Region, which belongs to a specific Country (in this case there is only one country: France).
This data is contained in a CSV file which I can read from on a row-by-row basis, however my goal is to convert this data into a tree structure (with France being at the root).
Each of these nodes will be given a specific Id value, which is something I've already gone and done, but the tricky part is that each node here must also contain a ParentId (for instance Belley and Gex need the ParentId of Ain, but Moulins and Vichy need the ParentId of Aller).
Below is a snippet of code I've written that has assigned an Id value to each name in this data set, along with some other values:
int id = 0;
List<CoverageAreaLevel> coverageAreas = GetCoverageAreaDataFromCsv(path, true);
List<LevelList> levelLists = new List<LevelList>
{
new LevelList { Names = coverageAreas.Select(a => a.Level1).Distinct().ToList(), Level = "1" },
new LevelList { Names = coverageAreas.Select(a => a.Level2).Distinct().ToList(), Level = "2" },
new LevelList { Names = coverageAreas.Select(a => a.Level3).Distinct().ToList(), Level = "3" },
new LevelList { Names = coverageAreas.Select(a => a.Level4).Distinct().ToList(), Level = "4" }
};
List<CoverageArea> newCoverageAreas = new List<CoverageArea>();
foreach (LevelList levelList in levelLists)
{
foreach (string name in levelList.Names)
{
CoverageArea coverageArea = new CoverageArea
{
Id = id++.ToString(),
Description = name,
FullDescription = name,
Level = levelList.Level
};
newCoverageAreas.Add(coverageArea);
}
}
The levelLists variable contains a sort-of heirarchical structure of the data that I'm looking for, but none of the items in that list are linked together by anything.
Any idea of how this could be implemented? I can manually figure out each ParentId, but I'd like to automate this process, especially if this needs to be done in the future.

The solution from #Camilo is really good and pragmatic. I would also suggest the use of a tree.
A sample implementation:
var countries = models.GroupBy(xco => xco.Country)
.Select((xco, index) =>
{
var country = new Tree<String>();
country.Value = xco.Key;
country.Children = xco.GroupBy(xr => xr.Region)
.Select((xr, xrIndex) =>
{
var region = new Tree<String>();
region.Value = xr.Key;
region.Parent = country;
region.Children =
xr.GroupBy(xd => xd.Department)
.Select((xd, index) =>
{
var department = new Tree<String>();
department.Value = xd.Key;
department.Parent = region;
department.Children = xd
.Select(xc => new Tree<String> { Value = xc.City, Parent = department });
return department;
});
return region;
});
return country;
});
public class Tree<T>
{
public IEnumerable<Tree<T>> Children;
public T Value;
public Tree<T> Parent;
}

One way you could solve this is by building dictionaries with the names and IDs of each level.
Assuming you have data like this:
var models = new List<Model>
{
new Model { Country = "France", Region = "FranceRegionA", Department = "FranceDept1", City = "FranceA" },
new Model { Country = "France", Region = "FranceRegionA", Department = "FranceDept1", City = "FranceB" },
new Model { Country = "France", Region = "FranceRegionA", Department = "FranceDept2", City = "FranceC" },
new Model { Country = "France", Region = "FranceRegionB", Department = "FranceDept3", City = "FranceD" },
new Model { Country = "Italy", Region = "ItalyRegionA", Department = "ItalyDept1", City = "ItalyA" },
new Model { Country = "Italy", Region = "ItalyRegionA", Department = "ItalyDept2", City = "ItalyB" },
};
You could do something like this, which can probably be improved further if needed:
var countries = models.GroupBy(x => x.Country)
.Select((x, index) => Tuple.Create(x.Key, new { Id = index + 1 }))
.ToDictionary(x => x.Item1, x => x.Item2);
var regions = models.GroupBy(x => x.Region)
.Select((x, index) => Tuple.Create(x.Key, new { ParentId = countries[x.First().Country].Id, Id = index + 1 }))
.ToDictionary(x => x.Item1, x => x.Item2);
var departments = models.GroupBy(x => x.Department)
.Select((x, index) => Tuple.Create(x.Key, new { ParentId = regions[x.First().Region].Id, Id = index + 1 }))
.ToDictionary(x => x.Item1, x => x.Item2);
var cities = models
.Select((x, index) => Tuple.Create(x.City, new { ParentId = departments[x.Department].Id, Id = index + 1 }))
.ToDictionary(x => x.Item1, x => x.Item2);
The main idea is to leverage the index parameter of the Select method and the speed of dictionaries to find the parent ID.
Sample output from a fiddle:
countries:
[France, { Id = 1 }],
[Italy, { Id = 2 }]
regions:
[FranceRegionA, { ParentId = 1, Id = 1 }],
[FranceRegionB, { ParentId = 1, Id = 2 }],
[ItalyRegionA, { ParentId = 2, Id = 3 }]
departments:
[FranceDept1, { ParentId = 1, Id = 1 }],
[FranceDept2, { ParentId = 1, Id = 2 }],
[FranceDept3, { ParentId = 2, Id = 3 }],
[ItalyDept1, { ParentId = 3, Id = 4 }],
[ItalyDept2, { ParentId = 3, Id = 5 }]
cities:
[FranceA, { ParentId = 1, Id = 1 }],
[FranceB, { ParentId = 1, Id = 2 }],
[FranceC, { ParentId = 2, Id = 3 }],
[FranceD, { ParentId = 3, Id = 4 }],
[ItalyA, { ParentId = 4, Id = 5 }],
[ItalyB, { ParentId = 5, Id = 6 }]

Change a flat collection of data into a nested tree hierarchy in C#

I have created a view that combines multiple foreign key tables.So the fetched data looks something like this:
Id Name TagId DepartmentId Code
1 N1 T1 NULL NULL
1 N1 T2 NULL NULL
1 N1 NULL D1 NULL
1 N1 NULL NULL C1
1 N1 NULL NULL C2
2 N2 T3 NULL NULL
2 N2 NULL D2 NULL
Want the result in model format like this:
[{
Id: 1,
Name: N1,
TagIds: [T1, T2],
DepartmentId: D1,
Codes: [C1, C2]
},
{
Id: 2,
Name: N2,
TagIds: [T3],
DepartmentId: D2,
Codes: []
}]
What is the most easy and efficient way to achieve this?

You haven't actually shown us what you've tried, but if you grab your entire view data into an IEnumerable into memory, you can use Linq's GroupBy to define groups, from which within you can use Linq filtering and projecting to map out the various properties in each Group.
I've assumed Id and Name have a 1:1 cardinality, so have used that in a Value Tuple grouping key. The output is projected to an anonymous type.
Your final output requires Json Serialization, but you can find any number of answers on SO to do that:
var groups = items.GroupBy(i => (i.Id, i.Name))
.Select(grp => new
{
grp.Key.Id,
grp.Key.Name,
TagIds = grp.Where(i => i.TagId != null)
.Select(x => x.TagId)
.ToArray(),
DepartmentId = grp.FirstOrDefault(i => i.DepartmentId != null)?.DepartmentId,
Codes = grp.Where(i => i.Code != null)
.Select(x => x.Code)
.ToArray(),
});
Test Data Here:
var items = new[]{
new {Id = 1, Name = "N1", TagId = "T1", DepartmentId = (string)null, Code = (string)null},
new {Id = 1, Name = "N1", TagId = "T2", DepartmentId = (string)null, Code = (string)null},
new {Id = 1, Name = "N1", TagId = (string)null, DepartmentId = "D1", Code = (string)null},
new {Id = 1, Name = "N1", TagId = (string)null, DepartmentId = (string)null, Code = "C1"},
new {Id = 1, Name = "N1", TagId = (string)null, DepartmentId = (string)null, Code = "C2"},
new {Id = 2, Name = "N2", TagId = "T3", DepartmentId = (string)null, Code = (string)null},
new {Id = 2, Name = "N2", TagId = (string)null, DepartmentId = "D2", Code = (string)null},
};
The output looks like so in LinqPad:

You can easily do it using Linq`s GroupBy method.
Here is a clean example:
var result = items.GroupBy(i => new { i.Id, i.Name })
.Select(g => new Result
{
Id = g.Key.Id,
Name = g.Key.Name,
TagIds = g.Select(i => i.TagId).ToList(),
DepartmentId = g.FirstOrDefault(i => i.DepartmentId != null)?.DepartmentId,
Codes = g.Select(i => i.Code).ToList();
});

Code to collapse duplicate and semi-duplicate records?

I have a list of models of this type:
public class TourDude {
public int Id { get; set; }
public string Name { get; set; }
}
And here is my list:
public IEnumerable<TourDude> GetAllGuides {
get {
List<TourDude> guides = new List<TourDude>();
guides.Add(new TourDude() { Name = "Dave Et", Id = 1 });
guides.Add(new TourDude() { Name = "Dave Eton", Id = 1 });
guides.Add(new TourDude() { Name = "Dave EtZ5", Id = 1 });
guides.Add(new TourDude() { Name = "Danial Maze A", Id = 2 });
guides.Add(new TourDude() { Name = "Danial Maze B", Id = 2 });
guides.Add(new TourDude() { Name = "Danial", Id = 3 });
return guides;
}
}
I want to retrieve these records:
{ Name = "Dave Et", Id = 1 }
{ Name = "Danial Maze", Id = 2 }
{ Name = "Danial", Id = 3 }
The goal mainly to collapse duplicates and near duplicates (confirmable by the ID), taking the shortest possible value (when compared) as name.
Where do I start? Is there a complete LINQ that will do this for me? Do I need to code up an equality comparer?
Edit 1:
var result = from x in GetAllGuides
group x.Name by x.Id into g
select new TourDude {
Test = Exts.LongestCommonPrefix(g),
Id = g.Key,
};
IEnumerable<IEnumerable<char>> test = result.First().Test;
string str = test.First().ToString();

If you want to group the items by Id and then find the longest common prefix of the Names within each group, then you can do so as follows:
var result = from x in guides
group x.Name by x.Id into g
select new TourDude
{
Name = LongestCommonPrefix(g),
Id = g.Key,
};
using the algorithm for finding the longest common prefix from here.
Result:
{ Name = "Dave Et", Id = 1 }
{ Name = "Danial Maze ", Id = 2 }
{ Name = "Danial", Id = 3 }
static string LongestCommonPrefix(IEnumerable<string> xs)
{
return new string(xs
.Transpose()
.TakeWhile(s => s.All(d => d == s.First()))
.Select(s => s.First())
.ToArray());
}

I was able to achieve this by grouping the records on the ID then selecting the first record from each group ordered by the Name length:
var result = GetAllGuides.GroupBy(td => td.Id)
.Select(g => g.OrderBy(td => td.Name.Length).First());
foreach (var dude in result)
{
Console.WriteLine("{{Name = {0}, Id = {1}}}", dude.Name, dude.Id);
}

Select multiple fields group by and sum

I want to do a query with linq (list of objects) and I really don't know how to do it, I can do the group and the sum but can't select rest of the fields.
Example:
ID Value Name Category
1 5 Name1 Category1
1 7 Name1 Category1
2 1 Name2 Category2
3 6 Name3 Category3
3 2 Name3 Category3
I want to group by ID, SUM by Value and return all fields like this.
ID Value Name Category
1 12 Name1 Category1
2 1 Name2 Category2
3 8 Name3 Category3

Updated :
If you're trying to avoid grouping for all the fields, you can group just by Id:
data.GroupBy(d => d.Id)
.Select(
g => new
{
Key = g.Key,
Value = g.Sum(s => s.Value),
Name = g.First().Name,
Category = g.First().Category
});
But this code assumes that for each Id, the same Name and Category apply. If so, you should consider normalizing as #Aron suggests. It would imply keeping Id and Value in one class and moving Name, Category (and whichever other fields would be the same for the same Id) to another class, while also having the Id for reference. The normalization process reduces data redundancy and dependency.

void Main()
{
//Me being lazy in init
var foos = new []
{
new Foo { Id = 1, Value = 5},
new Foo { Id = 1, Value = 7},
new Foo { Id = 2, Value = 1},
new Foo { Id = 3, Value = 6},
new Foo { Id = 3, Value = 2},
};
foreach(var x in foos)
{
x.Name = "Name" + x.Id;
x.Category = "Category" + x.Id;
}
//end init.
var result = from x in foos
group x.Value by new { x.Id, x.Name, x.Category}
into g
select new { g.Key.Id, g.Key.Name, g.Key.Category, Value = g.Sum()};
Console.WriteLine(result);
}
// Define other methods and classes here
public class Foo
{
public int Id {get;set;}
public int Value {get;set;}
public string Name {get;set;}
public string Category {get;set;}
}

If your class is really long and you don't want to copy all the stuff, you can try something like this:
l.GroupBy(x => x.id).
Select(x => {
var ret = x.First();
ret.value = x.Sum(xt => xt.value);
return ret;
}).ToList();
With great power great responsibility comes. You need to be careful. Line ret.value = x.Sum(xt => xt.value) will change your original collection, as you are passing reference, not new object. If you want to avoid it, you need to add some Clone method into your class like MemberwiseClone (but again, this will create shallow copy, so be careful). Afer that just replace the line with: var ret = x.First().Clone();

try this:
var objList = new List<SampleObject>();
objList.Add(new SampleObject() { ID = 1, Value = 5, Name = "Name1", Category = "Catergory1"});
objList.Add(new SampleObject() { ID = 1, Value = 7, Name = "Name1", Category = "Catergory1"});
objList.Add(new SampleObject() { ID = 2, Value = 1, Name = "Name2", Category = "Catergory2"});
objList.Add(new SampleObject() { ID = 3, Value = 6, Name = "Name3", Category = "Catergory3"});
objList.Add(new SampleObject() { ID = 3, Value = 2, Name = "Name3", Category = "Catergory3"});
var newList = from val in objList
group val by new { val.ID, val.Name, val.Category } into grouped
select new SampleObject() { ID = grouped.ID, Value = grouped.Sum(), Name = grouped.Name, Category = grouped.Category };
to check with LINQPad:
newList.Dump();