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Merge to various type List in to new List Type

I have 2 list
IEnumerable<int> Ids, IEnumerable<Guid> GuidIds
for sample data
IEnumerable<int> ids1 = new List<int>() { 1, 2, 4 };
IEnumerable<Guid> guidIds = new List<Guid>() { new Guid("F44D7A64-8BDE-41E1-810F-B24377AD7F94"), new Guid("F44D7A64-8BDE-41E1-810F-B24377AD7F96"), new Guid("F44D7A64-8BDE-41E1-810F-B24377AD7F97") };
and a class
public class ClassEnd
{
public int Id { get; set; }
public Guid GuidId { get; set; }
}
I want to merge into this by Linq query
IEnumerable<ClassEnd> mergeList = new List<ClassEnd>()
{
new ClassEnd() { Id = 1, CompanyId = new Guid("F44D7A64-8BDE-41E1-810F-B24377AD7F94") },
new ClassEnd() { Id = 2, CompanyId = new Guid("F44D7A64-8BDE-41E1-810F-B24377AD7F96") },
new ClassEnd() { Id = 3, CompanyId = new Guid("F44D7A64-8BDE-41E1-810F-B24377AD7F97") }
};
Could you please help me with how to merge like the above "mergeList" by using Linq?

If lists are of the same size - it can be easily achieved with Enumerable.Zip:
var classEnds = ids1
.Zip(guidIds, (i, guid) => new ClassEnd
{
Id = i,
GuidId = guid
})
.ToList();

List of descendant ID - children, grandchildren etc

CREATE TABLE [dbo].[Topic] (
[Id] SMALLINT NOT NULL,
[ParentId] SMALLINT NULL
);
I have a simple table (above) with a parent/child hierarchy. I'm using Entity Framework to extract the data. The number of rows is less than 100.
I want to get a list of descendant ID, consisting of the children, grandchildren and so on (possibly with the option of including the original root parent). As the table only contains a small number of rows, it's probably easier to extract all the data to a List<Topic> first and work on that, but I stand to be corrected.
The preferred output would be: Dictionary<int, List<int>>
Where the key would be the ID and the list would contain child/grandchild ID's
I've looked at tens and tens of solutions online but I can't find a solution that meets my needs. Can anyone help?

You could populate a dictionary with the ParentId->Id relations and use that to resolve sub-topics:
// prepare dictionary
var dictionary = new Dictionary<short, List<Topic>>();
// in real life this would get replaced by your database query
var topics = new List<Topic>
{
new Topic { Id = 1 },
new Topic { Id = 2, ParentId = 1 },
new Topic { Id = 3, ParentId = 1 },
new Topic { Id = 4, ParentId = 1 },
new Topic { Id = 5, ParentId = 1 },
new Topic { Id = 6, ParentId = 2 },
new Topic { Id = 7, ParentId = 2 },
new Topic { Id = 8, ParentId = 3 },
new Topic { Id = 9, ParentId = 4 },
new Topic { Id = 10, ParentId = 4 },
new Topic { Id = 11, ParentId = 8 },
new Topic { Id = 12, ParentId = 8 }
};
// populate dictionary with relations from DB
foreach(var topic in topics)
{
var key = topic.ParentId ?? -1;
if(!dictionary.ContainsKey(key))
{
dictionary.Add(key, new List<Topic>());
}
dictionary[key].Add(topic);
}
Now that you have the mappings available, you can write a simple recursive iterator method to resolve the descendants of a given id:
IEnumerable<short> GetDescendantIDs(short from)
{
if(dictionary.ContainsKey(from))
{
foreach(var topic in dictionary[from])
{
yield return topic.Id;
foreach(var child in GetDescendants(topic.Id))
yield return child;
}
}
}
// resolves to [1, 2, 6, 7, 3, 8, 11, 12, 4, 9, 10, 5]
var descendantsOfRoot = GetDescendantIDs(-1);
// resolves to [8, 11, 12]
var descendantsOfThree = GetDescendantIDs(3);
The Topic class used in the example above is just:
class Topic
{
internal short Id { get; set; }
internal short? ParentId { get; set; }
}

Consider that result has to be stored in tree:
public class TopicModel
{
public int Id { get; set; }
public int? ParentId{ get; set; }
public List<TopicModel> Children { get; set; };
}
Building tree:
// retrieveing from database
var plainResult = context.Topic
.Select(t => new TopicModel
{
Id = x.Id
ParentId = x.ParentId
})
.ToList();
var lookup = plainResult.Where(x => x.ParentId != null).ToLookup(x => x.ParentId);
foreach (c in plainResult)
{
if (lookup.Contains(c.Id))
{
c.Children = lookup[c.Id].ToList();
}
}
// here we have all root items with children intialized
var rootItems = plainResult.Where(x => x.ParentId == null).ToList();
And searching for children:
public static IEnumerable<TopicModel> GetAllChildren(TopicModel model)
{
if (model.Children != null)
{
foreach (var c in model.Children)
{
yield return c;
foreach (sc in GetAllChildren(c))
yield return sc;
}
}
}

how to dynamically create hierarchy of elements in json? c#

i have a method GetChild(id) that return the children with respect to id of parent passed as a parameter
those children can also have their own children to any level
if i want to create a JSON which represent the entire hierarchy of child and parent then how should i proceed?
public ActionResult GetChild(long id)
{
Dal objDal = new Dal();
var res = objDal.db.ChildGet(id).ToList();
return Json(res, JsonRequestBehavior.AllowGet);
}
this is justfor first level
how can i use this GetChild(id) method recursively?
any kind of help will be appreciated

public class Comment
{
public int Id { get; set; }
public int ParentId { get; set; }
public string Text { get; set; }
public List<Comment> Children { get; set; }
}
public JsonResult Test()
{
List<Comment> categories = new List<Comment>()
{
new Comment () { Id = 1, Text = "Yabancı Dil", ParentId = 0},
new Comment() { Id = 2, Text = "İngilizce", ParentId = 1 },
new Comment() { Id = 3, Text = "YDS", ParentId = 2 },
new Comment() { Id = 4, Text = "TOEFL", ParentId = 2 },
new Comment() { Id = 5, Text = "YDS Seviye1", ParentId = 3 },
new Comment() { Id = 6, Text = "TOEFL Seviye1", ParentId = 4 }
};
List<Comment> hierarchy = new List<Comment>();
hierarchy = categories
.Where(c => c.Id == 2)
.Select(c => new Comment()
{
Id = c.Id,
Text = c.Text,
ParentId = c.ParentId,
Children = GetChildren(categories, c.Id)
})
.ToList();
List<Comment> list = new List<Comment>();
List<string> list2 = new List<string>();
if (hierarchy != null)
{
liste.AddRange(hierarchy);
}
return Json(liste, JsonRequestBehavior.AllowGet);
}
public static List<Comment> GetChildren(List<Comment> comments, int parentId)
{
hAbDbContext db = new hAbDbContext();
return comments
.Where(c => c.ParentId == parentId)
.Select(c => new Comment()
{
Id = c.Id,
Text = c.Text,
ParentId = c.ParentId,
Children = GetChildren(comments, c.Id)
})
.ToList();
}

How can I convert a list of items with ParentID into a tree?

I'm using SQL Server and Entity Framework. On my database I have the following data:
ID | Name | ParentID
1 | Fire | null
2 | Fire2 | 1
3 | Fire3 | 2
4 | Blast | 2
5 | Water | null
6 | Water2 | 5
7 | WaterX | 5
I won't have massive data, so retrieving everything at once from the database is perfectly acceptable.
I want to retrieve this data and display on screen as a "tree".
Fire
Fire2
Fire3 Blast
Water
Water2 WaterX
How should I do this? Should I create some sort of recursion to render it? Should I somehow convert the list to an IGrouping?
I'm having trouble converting the flat list into something that I can render hierarchically on the screen, how could I do that?

This is the easiest way I know:
var things = new []
{
new { Id = 1, Name = "Fire", ParentId = (int?)null },
new { Id = 2, Name = "Fire2", ParentId = (int?)1 },
new { Id = 3, Name = "Fire3", ParentId = (int?)2 },
new { Id = 4, Name = "Blast", ParentId = (int?)2 },
new { Id = 5, Name = "Water", ParentId = (int?)null },
new { Id = 6, Name = "Water2", ParentId = (int?)5 },
new { Id = 7, Name = "Waterx", ParentId = (int?)5 }
};
var tree = things.ToLookup(x => x.ParentId, x => new { x.Id, x.Name });
The tree looks like this:
That should be fairly easy to render now.

If you can add another property to your class that has the child items like this:
public class Thing
{
public Thing()
{
Things = new List<Thing>();
}
public int Id { get; set; }
public string Name { get; set; }
public int? ParentId { get; set; }
public List<Thing> Things { get; set; }
}
Then you can easily group the items to their parents like this:
var things = new List<Thing>
{
new Thing { Id = 1, Name = "Fire", ParentId = null },
new Thing { Id = 2, Name = "Fire2", ParentId = 1 },
new Thing { Id = 3, Name = "Fire3", ParentId = 2 },
new Thing { Id = 4, Name = "Blast", ParentId = 2},
new Thing { Id = 5, Name = "Water", ParentId = null },
new Thing { Id = 6, Name = "Water2", ParentId = 5 },
new Thing { Id = 7, Name = "Waterx", ParentId = 6 }
};
var groupedThings = new List<Thing>();
foreach (var thing in things)
{
if (thing.ParentId != null)
{
things.First(t => t.Id == thing.ParentId).Things.Add(thing);
}
else
{
groupedThings.Add(thing);
}
}
groupedThings.Dump();

Linq to entities remove from list

I want to remove items from a list of entities, when there is a concidence from a list (id). I have written this code, but I am guessing there is a better way to do it, and improve performance.
Here is my code:
List<int> toRemove; //includes the ids of the entities to be removed
if (people.Count > 1)
people.RemoveAll(x => people.Any(y => y != x && toRemove.Contains(x.ID)));
else
people.RemoveAll(x => toRemove.Contains(x.ID));

Given a list of people, for example:
var people = new List<Person>
{
new Person { ID = 1, Name = "Fred1" },
new Person { ID = 2, Name = "Fred2" },
new Person { ID = 3, Name = "Fred3" },
new Person { ID = 4, Name = "Fred4" },
new Person { ID = 5, Name = "Fred5" },
new Person { ID = 6, Name = "Fred6" },
new Person { ID = 7, Name = "Fred7" },
new Person { ID = 8, Name = "Fred8" },
new Person { ID = 9, Name = "Fred9" },
new Person { ID = 10, Name = "Fred10" }
};
And a list of IDs to remove:
List<int> toRemove = new List<int> { 3, 4, 5 };
You can remove the unwanted entries like this:
people = people.Where(p => !toRemove.Contains(p.ID)).ToList();
Oh, and for completeness, here's a Person class to complete the example!
public class Person
{
public int ID { get; set; }
public string Name { get; set; }
}
And to show it working:
https://ideone.com/ERP3rk