I have list of classes and how to split, group them?
class CLA
{
string GroupName;
double Class;
double Value;
}
...
public List<List<CLA>> Dividr (List<CLA> a)
{
List<List<CLA> Clist = new List<List<CLA>>();
Clist.Addrange(...) //Here
returnn Clist;
}
As for dividing, it would be split by it's properties, GroupName, Class.
Example, if elements have same GroupName and Class it will be one List<>.
Simply use GroupBy. Then, as you want an inner list and not IEnumerable use ToList() for each group:
List<CLA> data = new List<CLA>();
var result = data.GroupBy(item => new { item.GroupName, item.Class })
.Select(group => group.ToList()).ToList();
Unless for specific reasons consider returning IEnumerable<IEnumerable<CLA>> instead - shame to already execute the query if not yet needed:
var result = data.GroupBy(item => new { item.GroupName, item.Class })
.Select(group => group);
Related
Below i have a snippet of code which outputs a list of Appointments based on clients, some clients can have more than one appointment but the latest one is the one that needs to be outputted for said client
the output is not grouping at all and for some reason i cannot figure why the heck not
foreach (ClientRecord client in clients)
{
List<ReturnRecord> records = db.Appointments
.AsNoTracking()
.Include(rec => rec.Property)
.Include(rec => rec.Property.Address)
.Include(rec => rec.AppointmentType)
.ToList()
.Where(rec => rec.ClientID == client.ID)
.Select(rec => new ReturnRecord
{
ClientName = $"{client.FirstNames} {client.Surnames}",
PropertyAddress = $"{rec.Property.Address.FormattedAddress}",
AppStatus = $"{rec.AppointmentStatus.Name}",
StockStatus = $"{rec.Property.Stocks.FirstOrDefault().StockStatus.Name}",
LastUpdated = rec.LastUpdated
})
.ToList();
returnList.AddRange(records);
}
returnList.GroupBy(rec => rec.PropertyAddress);
return Ok(returnList);
here is an attachment of the screen grab of the output
You need to assign result of GroupBy() to variable:
returnList = returnList.GroupBy(rec => rec.PropertyAddress).ToList();
Make sure to actually use the new IEnumerable that the .GroupBy() Method returned.
If you want to return a List you need to use a workaround:
Get the IEnumerable<IGrouping<int, ReturnRecord>> from the .GroupBy()
Use .SelectMany() to select all elements and save them into an IEnumerable
Now you can convert your IEnumerable into a List with .List()
Example:
// Longer Alternative
IEnumerable<IGrouping<int, ReturnRecord>> groups = resultList
.GroupBy((rec => rec.PropertyAddress);
IEnumerable<ReturnRecord> result = groups.SelectMany(group => group);
List<ReturnRecord> listResult = result.ToList();
return Ok(listResult);
// Shorter Alternative
IEnumerable<IGrouping<int, ReturnRecord>> groups = resultList
.GroupBy((rec => rec.PropertyAddress);
IEnumerable<ReturnRecord> result = groups.SelectMany(group => group);
return Ok(result.ToList());
Check the code bellow. Here i am creating a method that simply should remove the duplicate from the list foo. If you see the list values they are product id and quantity derived by : so the first part of number before : is product and and second part of number after : is the product quantity. I am taking this list into RemoveDuplicateItems() method for processing. This method should remove all matching product id items from whole list but my current method just returns exactly same list which i am taking on input. How can i fix my method to remove those item from list which has matching first part number. (first part number means before :)
The final output on doo variable it should remove the first from from list which is 22:15 since it has matching with second one.
C#:
[HttpPost]
public JsonResult DoSomething()
{
var foo = new List<string>();
foo.Add("22:10");//this should removed by RemoveDuplicateItems() since it has `22` matching with second one
foo.Add("22:15");
foo.Add("25:30");
foo.Add("26:30");
var doo = RemoveDuplicateItems(foo);
return Json("done");
}
public List<string> RemoveDuplicateItems(List<string> AllItems)
{
var FinalList = new List<string>();
var onlyProductIds = new List<string>();
foreach (var item in AllItems)
{
Match result = Regex.Match(item, #"^.*?(?=:)");
onlyProductIds.Add(result.Value);
}
var unique_onlyProductIds = onlyProductIds.Distinct().ToList();
foreach (var item in AllItems)
{
Match result = Regex.Match(item, #"^.*?(?=:)");
var id = unique_onlyProductIds.Where(x => x.Contains(result.Value)).FirstOrDefault();
if (id != null)
{
FinalList.Add(item);
}
}
return FinalList;
}
Does this work for you?
List<string> doo =
foo
.Select(x => x.Split(':'))
.GroupBy(x => x[0], x => x[1])
.Select(x => $"{x.Key}:{x.Last()}")
.ToList();
There are multiple ways to achieve this, one is, as suggested by #Aluan Haddad is to use Linq. His comment uses the query syntax but would could use the method syntax too (I assumed you use C#8):
List<string> doo = foo.GroupBy(str => str[0..2])
.Select(entry => entry.Last())
.ToList();
Note that this works because the current implementation of GroupBy preserves ordering.
you can do it using Linq :
var doo = foo.Select(x =>
{
var split = x.Split(':');
return new { Key = split[0], Value = split[1] };
})
.GroupBy(x => x.Key)
.OrderBy(x => x.Key)
.Select(x =>
{
var max = x.LastOrDefault();
return $"{max.Key}:{max.Value}";
}
).ToList();
I need to remove duplicates, but also log which I am removing. I have two solutions right now, one that can go through each duplicate and one that removes duplicates. I know that removing in-place inside a foreach is dangerous so I am a bit stuck on how to do this as efficient as possible.
What I got right now
var duplicates = ListOfThings
.GroupBy(x => x.ID)
.Where(g => g.Skip(1).Any())
.SelectMany(g => g);
foreach (var duplicate in duplicates)
{
Log.Append(Logger.Type.Error, "Conflicts with another", "N/A", duplicate.ID);
}
ListOfThings = ListOfThings.GroupBy(x => x.ID).Select(y => y.First()).ToList();
Well, ToList() will materialize the query, so if you allow side effects (i.e. writing to log) it could be like that:
var cleared = ListOfThings
.GroupBy(x => x.ID)
.Select(chunk => {
// Side effect: writing to log while selecting
if (chunk.Skip(1).Any())
Log.Append(Logger.Type.Error, "Conflicts with another", "N/A", chunk.Key);
// if there're duplicates by Id take the 1st one
return chunk.First();
})
.ToList();
Why group when one can use the Aggregate function to determine the duplicates for the report and the result?
Example
var items = new List<string>() { "Alpha", "Alpha", "Beta", "Gamma", "Alpha"};
var duplicatesDictionary =
items.Aggregate (new Dictionary<string, int>(),
(results, itm) =>
{
if (results.ContainsKey(itm))
results[itm]++;
else
results.Add(itm, 1);
return results;
});
Here is the result of the above where each insert was counted and reported.
Now extract the duplicates report for any count above 1.
duplicatesDictionary.Where (kvp => kvp.Value > 1)
.Select (kvp => string.Format("{0} had {1} duplicates", kvp.Key, kvp.Value))
Now the final result is to just extract all the keys.
duplicatesDictionary.Select (kvp => kvp.Key);
You can use a hash set and union it with a list to get unique items; just override the reference comparison. Implementing IEqualityComparer<T> is flexible; if it's just ID that makes two objects unique then ok; but if it's more you can extend it, too.
You can get duplicates with LINQ.
void Main()
{
//your original class:
List<Things> originalList = new List<Things> { new Things(5), new Things(3), new Things(5) };
//i'm doing this in LINQPad; if you're using VS you may need to foreach the object
Console.WriteLine(originalList);
//put your duplicates back in a list and log them as you did.
var duplicateItems = originalList.GroupBy(x => x.ID).Where(x => x.Count() > 1).ToList();//.Select(x => x.GetHashCode());
Console.WriteLine(duplicateItems);
//create a custom comparer to compare your list; if you care about more than ID then you can extend this
var tec = new ThingsEqualityComparer();
var listThings = new HashSet<Things>(tec);
listThings.UnionWith(originalList);
Console.WriteLine(listThings);
}
// Define other methods and classes here
public class Things
{
public int ID {get;set;}
public Things(int id)
{
ID = id;
}
}
public class ThingsEqualityComparer : IEqualityComparer<Things>
{
public bool Equals(Things thing1, Things thing2)
{
if (thing1.ID == thing2.ID)
{
return true;
}
else
{
return false;
}
}
public int GetHashCode(Things thing)
{
int hCode = thing.ID;
return hCode.GetHashCode();
}
}
I have an object that has a list of another object in it. i.e Object1 contains List<Object2>.
Assuming this is the definition of object 2:
public class Object2
{
string code,
string name,
decimal amount
}
I want to be a able to make a list2 from the list whose value will contain what something similar to what a select name, code, sum(amount) group by code kinda statement could have given me
this is what i did but it didnt contain what i needed on passing through.
var newlist = obj2List.GroupBy(x => x.code)
.Select(g => new { Amount = g.Sum(x => x.amount) });
I want code and name in the new list just like the sql statement above.
You're almost there:
var newlist = obj2List.GroupBy(x => x.code)
.Select(g => new
{
Code = g.First().code,
Name = g.First().name,
Amount = g.Sum(x => x.amount)
});
This groups the items by code and creates an anonymous object for each group, taking the code and name of first item of the group. (I assume that all items with the same code also have the same name.)
If you are grouping by code and not by name you'd have to choose something for name from the list, perhaps with First() or Last() or something.
var newlist = obj2List.GroupBy(x => x.code).Select(g => new {
Code = g.Key,
Name = g.First().name,
Amount = g.Sum(x => x.amount)
});
var query = Object1.Obj2List
.GroupBy(obj2 => obj2.code)
.Select(g => new {
Names = string.Join(",", g.Select(obj2.name)),
Code = g.Key,
Amount = g.Sum(obj2 => obj2.Amount)
});
Since you group by code only you need to aggregate the name also in some way. I have used string.Join to create a string like "Name1,Name2,Name3" for each code-group.
Now you could consume the query for example with a foreach:
foreach(var x in query)
{
Console.WriteLine("Code: {0} Names: {1} Amount: {2}"
, x.Code, x.Names, x.Amount);
}
Instead of using the LINQ Extension Methods .GroupBy() and .Select() you could also use a pure LINQ statement which is way easier to read if you come from a SQL Background.
var ls = new List<Object2>();
var newLs = from obj in ls
group obj by obj.code into codeGroup
select new { code = codeGroup.Key, amount = codeGroup.Sum(s => s.amount) };
I am trying to determine if there is a better way to execute the following query:
I have a List of Pair objects.
A Pair is defined as
public class Pair
{
public int IDA;
public int IDB;
public double Stability;
}
I would like to extract a list of all distinct ID's (ints) contained in the List<Pair>.
I am currently using
var pIndices = pairs.SelectMany(p => new List<int>() { p.IDA, p.IDB }).Distinct().ToList();
Which works, but it seems unintuitive to me to create a new List<int> only to have it flattened out by SelectMany.
This is another option I find unelegant to say the least:
var pIndices = pairs.Select(p => p.IDA).ToList();
pIndices.AddRange(pairs.Select((p => p.IDB).ToList());
pIndices = pIndices.Distinct().ToList();
Is there a better way? And if not, which would you prefer?
You could use Union() to get both the A's and B's after selecting them individually.
var pIndices = pairs.Select(p => p.IDA).Union(pairs.Select(p => p.IDB));
You could possibly shorten the inner expression to p => new [] { p.IDA, p.IDB }.
If you don't want to create a 2-element array/list for each Pair, and don't want to iterate your pairs list twice, you could just do it by hand:
HashSet<int> distinctIDs = new HashSet<int>();
foreach (var pair in pairs)
{
distinctIDs.Add(pair.IDA);
distinctIDs.Add(pair.IDB);
}
This is one without a new collection:
var pIndices = pairs.Select(p => p.IDA)
.Concat(pairs.Select(p => p.IDB))
.Distinct();
Shorten it like this:
var pIndices = pairs.SelectMany(p => new[] { p.IDA, p.IDB }).Distinct().ToList();
Using Enumerable.Repeat is a little unorthodox, but here it is anyway:
var pIndices = pairs
.SelectMany(
p => Enumerable.Repeat(p.IDA, 1).Concat(Enumerable.Repeat(p.IDB, 1))
).Distinct()
.ToList();
Finally, if you do not mind a little helper class, you can do this:
public static class EnumerableHelper {
// usage: EnumerableHelper.AsEnumerable(obj1, obj2);
public static IEnumerable<T> AsEnumerable<T>(params T[] items) {
return items;
}
}
Now you can do this:
var pIndices = pairs
.SelectMany(p => EnumerableHelper.AsEnumerable(p.IDA, p.IDB))
.Distinct()
.ToList();