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How to concatenate multiple rows list with same value into single row

I have the following class called "Person".
public class Person
{
public int Id { get; set; }
public string Name { get; set; }
public string Hobby { get; set; }
}
I created a list with the following data:
List<Person> users = new List<Person>()
{
new Person {Id= 1, Name = "Silva", Hobby = "Football" },
new Person {Id= 2, Name = "Bob", Hobby = "Golf"},
new Person {Id= 2, Name = "Bob", Hobby = "Tennis"},
new Person {Id= 1, Name = "Silva", Hobby = "Sleeping"},
new Person {Id= 3, Name = "Sue", Hobby = "Drinking"}
new Person {Id= 1, Name = "Silva", Hobby = "Handball"},
new Person {Id= 3, Name = "Sue", Hobby = "Football"},
};
Now I need to create a new list called "usersHobbies" that when called returns the following result.
Id Name Hobby
1 Silva Football, Sleeping, Handball
2 Bob Golf, Tennis
3 Sue Drinking, Football

You would use GroupBy() to achieve that. Group by Id, select the Name from the first group, use string.Join() to join the Hobbies into a single string:
var result = users.GroupBy(u => u.Id) // group by Id
.Select(g => new // select values
{
Id = g.Key,
Name = g.First().Name,
Hobbies = string.Join(", ", g.Select(u => u.Hobby))
})
.ToList();
Output:
If you want to return a new Person instead of an anonymous type, just update the Select:
.Select(g => new Person
{
Id = g.Key,
Name = g.First().Name,
Hobby = string.Join(", ", g.Select(u => u.Hobby))
})
Update from your comment:
is it possible instead of string.join() to return a list or array
Yes, it is. Using an anonymous type:
var result = users.GroupBy(u => u.Id) // group by Id
.Select(g => new // select values
{
Id = g.Key,
Name = g.First().Name,
Hobbies = g.Select(u => u.Hobby).ToList()
})
.ToList();
Which returns a List<string> for Hobbies.

.GroupBy() has an override that lets you define a key selector, an element selector and the result selector (docs), which could suit your use case:
var result = users
.GroupBy(
u => new { u.Id, u.Name }, // key selector
u => u.Hobby, // element selector
(user, hobbies) => new Person {
Id = user.Id,
Name = user.Name,
Hobby = string.Join(", ", hobbies) })
.ToList();
Here, (user, hobbies) are referencing the key selector and the element selector, respectively.
What happens is:
the users are grouped into unique users based on the combination of Id and Name (key selector)
the hobbies of each unique user are collected into an IEnumerable<string> (element selector)
for each unique user, a Person object is created and populated with all of the users hobbies.

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 }]

Convert data collection into nested hierarchical object list

I'm wanting to make an API call that gets all the unique survey IDs and put them into an array with total answer counts based on the unique answer value and list of user ids. For example: ICollection<Survey>
ID Survey_Id Answer User
1 Apple_Survey 1 Jones
2 Apple_Survey 1 Smith
3 Banana_Survey 2 Smith
4 Apple_Survey 3 Jane
5 Banana_Survey 2 John
The API result I currently have:
{Data: [
{
survey_id: "Apple_Survey",
answer: "1",
user: "Jones"
},
...
]}
Where I get stuck is in the code to process the data:
foreach (var info in data
.GroupBy(x => x.Survey_Id)
.Select(group => new { SurveyId = group.Key,
Count = group.Count() }) )
{
Console.WriteLine("{0} {1}", info.SurveyId, info.Count);
//Result: Apple_Survey 3 Banana_Survey 2
}
Ideal results:
{Data: [
{
survey_id: "Apple_Survey",
answers: [//Example: rating answer would be 1-10, not an ID
{answer: "1", count: 2, users: ["Jones", "Smith"]},
{answer: "3", count: 1, users: ["Jane"]}
]
},
...
]}
How can I get the distinct answers based on survey_id and the list of users based on the answer? Any help would be greatly appreciated!

See if following helps :
class Program
{
static void Main(string[] args)
{
List<Survey> surveys = new List<Survey>() {
new Survey() { ID = 1, Survey_Id = "Apple_Survey", Answer = 1, User = "Jones"},
new Survey() { ID = 2, Survey_Id = "Apple_Survey", Answer = 1, User = "Smith"},
new Survey() { ID = 3, Survey_Id = "Banana_Survey", Answer = 2, User = "Smith"},
new Survey() { ID = 4, Survey_Id = "Apple_Survey", Answer = 3, User = "Jane"},
new Survey() { ID = 5, Survey_Id = "Banana_Survey", Answer = 2, User = "John"}
};
var results = surveys.GroupBy(x => x.Survey_Id).Select(x => x.GroupBy(y => y.Answer)
.Select(y => new { answer = y.Key, count = y.Count(), users = y.Select(z => z.User).ToList()}).ToList())
.ToList();
}
}
public class Survey
{
public int ID { get; set; }
public string Survey_Id { get; set; }
public int Answer { get; set; }
public string User { get; set; }
}

A simple way is based on sql only.. you could use a query as :
select Survey_Id, Answer, COUNT(*) answer_count, group_concat(user) answer_user
from my_table
group Survey_Id, Answer

I'd go for
table.GroupBy( x => x.Survey_Id ).Select( x => new { Survey_Id=x.Key, Answers=x.GroupBy( y => y.Answer ).Select( y => new { Answer=y.Key, Count=y.Count(), Users=y.Select( z => z.User)})} )
That creates an ienumerable of pairs of a survey and an ienumerable of answers, each with its count and an ienumerable of the users that voted for that answer.
Try it out on dotnetfiddle.net!

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();
});

Add duplicates together in List

First question :)
I have a List<Materiau> (where Materiau implements IComparable<Materiau>), and I would like to remove all duplicates and add them together
(if two Materiau is the same (using the comparator), merge it to the first and remove the second from the list)
A Materiau contains an ID and a quantity, when I merge two Materiau using += or +, it keeps the same ID, and the quantity is added
I cannot control the input of the list.
I would like something like this:
List<Materiau> materiaux = getList().mergeDuplicates();
Thank you for your time :)

Check out Linq! Specifically the GroupBy method.
I don't know how familiar you are with sql, but Linq lets you query collections similarly to how sql works.
It's a bit in depth to explain of you are totally unfamiliar, but Code Project has a wonderful example
To sum it up:
Imagine we have this
List<Product> prodList = new List<Product>
{
new Product
{
ID = 1,
Quantity = 1
},
new Product
{
ID = 2,
Quantity = 2
},
new Product
{
ID = 3,
Quantity = 7
},
new Product
{
ID = 4,
Quantity = 3
}
};
and we wanted to group all the duplicate products, and sum their quantities.
We can do this:
var groupedProducts = prodList.GroupBy(item => item.ID)
and then select the values out of the grouping, with the aggregates as needed
var results = groupedProducts.Select( i => new Product
{
ID = i.Key, // this is what we Grouped By above
Quantity = i.Sum(prod => prod.Quantity) // we want to sum up all the quantities in this grouping
});
and boom! we have a list of aggregated products

Lets say you have a class
class Foo
{
public int Id { get; set; }
public int Value { get; set; }
}
and a bunch of them inside a list
var foocollection = new List<Foo> {
new Foo { Id = 1, Value = 1, },
new Foo { Id = 2, Value = 1, },
new Foo { Id = 2, Value = 1, },
};
then you can group them and build the aggregate on each group
var foogrouped = foocollection
.GroupBy( f => f.Id )
.Select( g => new Foo { Id = g.Key, Value = g.Aggregate( 0, ( a, f ) => a + f.Value ) } )
.ToList();

List<Materiau> distinctList = getList().Distinct(EqualityComparer<Materiau>.Default).ToList();