Develop Reference

Find all duplicates in a list in C#

I have a Custom class shown below
internal class RecurringClusterModel
{
public int? From { get; set; }
public int? To { get; set; }
public string REC_Cluster_1 { get; set; }
public string REC_Cluster_2 { get; set; }
public string REC_Cluster_3 { get; set; }
public string REC_Cluster_4 { get; set; }
public string REC_Cluster_5 { get; set; }
public string REC_Cluster_6 { get; set; }
public string REC_Cluster_7 { get; set; }
public string REC_Cluster_8 { get; set; }
public string REC_Cluster_9 { get; set; }
public string REC_Cluster_10 { get; set; }
I have a List of this class
List<RecurringClusterModel> recurringRecords = new List<RecurringClusterModel>();
The data can be in the below format
recurringRecords[0].REC_Cluster_1 = "USA";
recurringRecords[0].REC_Cluster_2 = "UK";
recurringRecords[0].REC_Cluster_3 = "India";
recurringRecords[0].REC_Cluster_4 = "France";
recurringRecords[0].REC_Cluster_5 = "China";
recurringRecords[1].REC_Cluster_1 = "France";
recurringRecords[1].REC_Cluster_2 = "Germany";
recurringRecords[1].REC_Cluster_3 = "Canada";
recurringRecords[1].REC_Cluster_4 = "Russia";
recurringRecords[1].REC_Cluster_5 = "India";
....
I want to find the duplicate records between all the Cluster properties..This is just a subset I have 50 properties till REC_Cluster_50. I want to find out which countries are getting duplicated between the 50 cluster properties of the list.
So in this case India and France are getting duplicated. I can group by individual property and then find out the duplicate by getting the count but then I d have to do it for all the 50 Rec_Clusters property. Not sure if there is a better way of doing it.
Thanks

Since you want to capture the From and To, I suggest you structure your class like this:
internal class RecurringClusterModel
{
public int? From { get; set; }
public int? To { get; set; }
public IEnumerable<string> REC_Clusters { get; set; }
}
Then you can search for duplicates:
var dupes = recs
.Select(r => new
{
r.From,
r.To,
DuplicateClusters = r.REC_Clusters.GroupBy(c => c)
.Where(g => g.Count() > 1) // duplicates
.SelectMany(g => g) // flatten it back
.ToArray() // indexed
})
.Where(r => r.DuplicateClusters.Any()) //only interested in clusters with duplicates
.ToArray();
EDIT
If you want all duplicates, then it will be:
var allDupes = recs.SelectMany(r => r.REC_Clusters)
.Select(r => r.GroupBy(c => c)
.Where(g => g.Count() > 1)
.SelectMany(g => g))
.Where(r => r.Any()).ToArray();
But now you lose track of the From/To

I would add an enumerable to your class that iterates over all properties of that class:
internal class RecurringClusterModel
{
public string REC_Cluster_1 { get; set; }
public string REC_Cluster_2 { get; set; }
public string REC_Cluster_3 { get; set; }
public IEnumerable<string> Clusters => GetAllClusters();
private IEnumerable<string> GetAllClusters()
{
if (!string.IsNullOrEmpty(REC_Cluster_1))
yield return REC_Cluster_1;
if (!string.IsNullOrEmpty(REC_Cluster_2))
yield return REC_Cluster_2;
if (!string.IsNullOrEmpty(REC_Cluster_3))
yield return REC_Cluster_3;
}
}
With this you can flatten the list to the individual clusters and then group by. If you need the original object back again, you have to provide it while flattening. Here is an example:
var clusters = Enumerable
.Range(1, 10)
.Select(_ => new RecurringClusterModel
{
REC_Cluster_1 = _Locations[_Random.Next(_Locations.Count)],
REC_Cluster_2 = _Locations[_Random.Next(_Locations.Count)],
REC_Cluster_3 = _Locations[_Random.Next(_Locations.Count)],
})
.ToList();
var dictionary = clusters
// Flatten the list and preserve original object
.SelectMany(model => model.Clusters.Select(cluster => (cluster, model)))
// Group by flattened value and put original object into each group
.GroupBy(node => node.cluster, node => node.model)
// Take only groups with more than one element (duplicates)
.Where(group => group.Skip(1).Any())
// Depending on further processing you could put the groups into a dictionary.
.ToDictionary(group => group.Key, group => group.ToList());
foreach (var cluster in dictionary)
{
Console.WriteLine(cluster.Key);
foreach (var item in cluster.Value)
{
Console.WriteLine(" " + String.Join(", ", item.Clusters));
}
}

Convert SQL to Linq with EF Core

I am using .NET Core 2.2, EF Core, C# and SQL Server 2017.
I am not able to translate the query I need to Linq.
This is the query I need to convert:
SELECT TOP 5
p.Id,
p.Title,
AVG(q.RatingValue) AvgRating
FROM Movies AS p
INNER JOIN Ratings AS q ON p.Id = q.MovieId
GROUP BY p.Id, p.Title
ORDER BY AvgRating DESC, p.Title ASC
The idea of the previous query is to get the Top 5 movies according to the Avg rating, ordering it by the highest average first, and in case of same average order alphabetically.
So far this is my query that makes the join, but then still missing: the group by, average, and ordering:
public class MovieRepository : IMovieRepository
{
private readonly MovieDbContext _moviesDbContext;
public MovieRepository(MovieDbContext moviesDbContext)
{
_moviesDbContext = moviesDbContext;
}
public IEnumerable<Movie> GetTopFive()
{
var result = _moviesDbContext.Movies.OrderByDescending(x => x.Id).Take(5).
Include(x => x.Ratings);
return result;
}
}
And these are the entities:
public class Movie
{
public int Id { get; set; }
public string Title { get; set; }
public int YearOfRelease { get; set; }
public string Genre { get; set; }
public int RunningTime { get; set; }
public IList<Rating> Ratings { get; set; }
}
public class Rating
{
public int Id { get; set; }
public int MovieId { get; set; }
public int UserId { get; set; }
public decimal RatingValue { get; set; }
}
I tried to use Linqer tool also to convert my query to Linq, but it was not working.
I will appreciate any help to convert that query to LINQ for the method "GetTopFive".
Thanks

Try this one -
var data = _moviesDbContext.Movies.Include(x => x.Ratings)
.Select(x => new {
Id = x.Id,
Title = x.Title,
Average = (int?)x.Ratings.Average(y => y.RatingValue)
}).OrderByDescending(x => x.Average).ThenBy(x => x.Title).Take(5).ToList();

Try as follows:
public IEnumerable<Movie> GetTopFive()
{
var result = _moviesDbContext.Ratings.GroupBy(r => r.MovieId).Select(group => new
{
MovieId = group.Key,
MovieTitle = group.Select(g => g.Movie.Title).FirstOrDefault(),
AvgRating = group.Average(g => g.RatingValue)
}).OrderByDescending(s => s.AvgRating).Take(5).ToList();
return result;
}
This will exclude the movies having no ratings.
But if you do as follows (as artista_14's answer):
public IEnumerable<Movie> GetTopFive()
{
var result = _moviesDbContext.Movies.GroupBy(x => new { x.Id, x.Title })
.Select(x => new {
Id = x.Key.Id,
Title = x.Key.Title,
Average = x.Average(y => y.Ratings.Sum(z => z.RatingValue))
}).OrderByDescending(x => x.Average).ThenBy(x => x.Title).Take(5).ToList();
return result;
}
this will include the movies having no ratings also.
Note: I see your Rating model class does not contain any Movie navigation property. Please add this as follows:
public class Rating
{
public int Id { get; set; }
public int MovieId { get; set; }
public int UserId { get; set; }
public decimal RatingValue { get; set; }
public Movie Movie { get; set; }
}

and finally this is the code working nicely:
var data = _moviesDbContext.Movies.Include(x => x.Ratings)
.Select(x => new MovieRating
{
Id = x.Id,
Title = x.Title,
Average = x.Ratings.Average(y => y.RatingValue)
}).OrderByDescending(x => x.Average).ThenBy(x => x.Title).Take(5).ToList();
return data;
The problem was creating an anonymous type in the select, so this line resolves the issue: .Select(x => new MovieRating
And this is the complete code for the method and the new class I have created to map the select fields with a concrete type:
public class MovieRepository : IMovieRepository
{
private readonly MovieDbContext _moviesDbContext;
public MovieRepository(MovieDbContext moviesDbContext)
{
_moviesDbContext = moviesDbContext;
}
public IEnumerable<Movie> GetAll()
{
return _moviesDbContext.Movies;
}
public IEnumerable<MovieRating> GetTopFive()
{
var result = _moviesDbContext.Movies.Include(x => x.Ratings)
.Select(x => new MovieRating
{
Id = x.Id,
Title = x.Title,
Average = x.Ratings.Average(y => y.RatingValue)
}).OrderByDescending(x => x.Average).ThenBy(x => x.Title).Take(5).ToList();
return result;
}
}
public class MovieRating
{
public int Id { get; set; }
public string Title { get; set; }
public decimal Average { get; set; }
}

Sorting and Updating a Generic List of Object based on a Sub Object

I have the following objects:
public class TestResult
{
public string SectionName { get; set; }
public int Score { get; set; }
public int MaxSectionScore { get; set; }
public bool IsPartialScore { get; set; }
public string Name { get; set; }
public int NumberOfAttempts { get; set; }
}
public class TestResultGroup
{
public TestResultGroup()
{
Results = new List<TestResult>();
Sections = new List<string>();
}
public List<TestResult> Results { get; set; }
public List<string> Sections { get; set; }
public string Name { get; set; }
public int Rank { get; set; }
}
So, a TestResultGroup can have any number of results of type TestResult. These test results only differ by their SectionName.
I have a List<TestResultGroup> which I need to sort into descending order based on a score in the Results property, but only when Results has an item whos SectionName = "MeanScore" (if it doesnt have this section we can assume a score of -1). How would I go about ordering the list? Ideally I would also like to apply the result of this ordering to the Rank property.
Many Thanks

List<TestResultGroup> groups = ...
// group test result groups by the same score and sort
var sameScoreGroups = groups.GroupBy(
gr =>
{
var meanResult = gr.Results.FirstOrDefault(res => res.SectionName == "MeanScore");
return meanResult != null ? meanResult.Score : -1;
})
.OrderByDescending(gr => gr.Key);
int rank = 1;
foreach (var sameScoreGroup in sameScoreGroups)
{
foreach (var group in sameScoreGroup)
{
group.Rank = rank;
}
rank++;
}
// to obtain sorted groups:
var sortedGroups = groups.OrderByDescending(gr => gr.Rank).ToArray();
Or even write one expression with a side effect:
List<TestResultGroup> groups = ...
int rank = 1;
var sortedGroups = groups
.GroupBy(
gr =>
{
var meanResult = gr.Results.FirstOrDefault(res => res.SectionName == "MeanScore");
return meanResult != null ? meanResult.Score : -1;
})
.OrderByDescending(grouping => grouping.Key)
.SelectMany(grouping =>
{
int groupRank = rank++;
foreach (var group in grouping)
{
group.Rank = groupRank;
}
return grouping;
})
.ToArray(); // or ToList

Query multiple tables and send query to Dictionary

I'm trying to query multiple table and save the query as a global dictionary for further processing. I've tried the following, but instead of values I get the class name in the dictionary. Please take a look and show me what's wrong and where to read up more on todictionary queries?
public class linqtosql
{
public Dictionary<int, MC_VARIABLES> dctMC = new Dictionary<int, MC_VARIABLES>();
public class MC_VARIABLES
{
public int ID { get; set; }
public int UDLY_LAST { get; set; }
public int STRIKE { get; set; }
public decimal SKEW_A { get; set; }
public decimal SKEW_B { get; set; }
public double SKEW_C { get; set; }
}
public void GET_DATA()
{
var qryBOOK = from B in Globals.DATA.BOOKs
from O in Globals.DATA.OPTIONs
from U in Globals.DATA.UDLies
from S in Globals.DATA.SKEWs
where B.CONTRACT == O.CONTRACT
where O.UDLY_SYMBOL == U.UDLY_SYMBOL
where O.CONTRACT == S.CONTRACT
select new MC_VARIABLES
{ ID = B.ID, STRIKE = (int)B.STRIKE, SKEW_A = (decimal)S.SKEW_A };
dctMC = qryBOOK.ToDictionary(x => x.ID, x => x);
foreach (KeyValuePair<int, MC_VARIABLES> KVP in dctMC)
{
var key = KVP.Key;
var item = KVP.Value.SKEW_A;
}
}
}

it should be x => x instead of x => MC_VARIABLES, x is of type MC_VARIABLES in this case.
qryBOOK.ToDictionary(x => x.ID, x => x)

LINQ OrderBy with multiple layers

Suppose I have a class like this:
public class TestParent
{
public string ParentID { get; set; }
public List<TestGroup> GroupItems { get; set; }
}
public class TestGroup
{
public string GroupID { get; set; }
}
How can I sort an object of type TestParent by ParentID and all the TestGroups in it by GroupID?
I could do it with this code:
for (int i = 0; i < ResponseArray.Count; i++ )
{
ResponseArray[i].GroupItems = ResponseArray[i].GroupItems
.OrderBy(x => x.GroupID)
.ToList();
}
return ResponseArray.OrderBy(x => x.GroupID).ToList();
It is possible to archieve the same using only LINQ?

You can use Select after the OrderBy and order the GroupItems inside that:
ResponseArray.OrderBy(t => t.ParentID).Select(t => new TestParent()
{
ParentID = t.ParentID,
GroupItems = t.GroupItems.OrderBy(g => g.GroupID).ToList()
})