I have the following result:
var result = (from p1 in db.Table
select new ReportInform
{
DataValue = p1.DataValue,
SampleDate = p1.SampleDate
})
.Distinct()
.ToList();
// Next getting list of duplicate SampleDates
var duplicates = result.GroupBy(x => x.SampleDate)
.Where(g => g.Count() > 1)
.Select (x => x)
.ToList();
foreach (var r in result)
{
if (duplicates.Contains(r.SampleDate)) // get error here on incompatbility
{
r.SampleDate = r.SampleDate.Value.AddMilliseconds(index++);
}
}
Cannot convert from 'System.DateTime?' to 'System.Linq.IGrouping
That error is pretty clear but may not be at a first glance. As a programmer, you need to learn how to read, understand and make sense of compiler or runtime errors.
Anyhow it is complaining that it cannot convert DateTime? to System.Linq.IGrouping<System.DateTime, ReportInForm>. Why? Because this query returns an System.Linq.IGrouping<System.DateTime, ReportInForm>
var duplicates = result.GroupBy(x => x.SampleDate)
.Where(g => g.Count() > 1)
.Select (x => x)
.ToList();
The GroupBy method returns IGrouping<System.DateTime, ReportInForm> which has a Key and the Key is the thing you grouped by and a list of items in that group. You are grouping by SampleDate and checking if there are more than one items in that group and then selecting the group. Thus dulplicates has a list of IGrouping<System.DateTime, ReportInForm> and you are asking the runtime to check if it contains a DateTime? and it blows up at this line:
duplicates.Contains(r.SampleDate)
One way to fix this is: What you want to do is to select the key of that group. Thus do this:
.Select (x => x.Key)
If you are expecting duplicates to be of type List<DateTime?> then you meant to write this
.Select(x => x.Key)
instead of
.Select(x => x)
Related
So far, I have this:
var v = Directory.EnumerateFiles(_strConfigurationFolder)
.GroupBy(x => GetReportName(Path.GetFileNameWithoutExtension(x)));
Configuration folder will contain pairs of files:
abc.json
abc-input.json
def.json
def-input.json
GetReportName() method strips off the "-input" and title cases the filename, so you end up with a grouping of:
Abc
abc.json
abc-input.json
Def
def.json
def-input.json
I have a ReportItem class that has a constructor (Name, str1, str2). I want to extend the Linq to create the ReportItems in a single statement, so really something like:
var v = Directory.EnumerateFiles(_strConfigurationFolder)
.GroupBy(x => GetReportName(Path.GetFileNameWithoutExtension(x)))
**.Select(x => new ReportItem(x.Key, x[0], x[1]));**
Obviously last line doesn't work because the grouping doesn't support array indexing like that. The item should be constructed as "Abc", "abc.json", "abc-input.json", etc.
If you know that each group of interest contains exactly two items, use First() to get the item at index 0, and Last() to get the item at index 1:
var v = Directory.EnumerateFiles(_strConfigurationFolder)
.GroupBy(x => GetReportName(Path.GetFileNameWithoutExtension(x)))
.Where(g => g.Count() == 2) // Make sure we have exactly two items
.Select(x => new ReportItem(x.Key, x.First(), x.Last()));
var v = Directory.EnumerateFiles(_strConfigurationFolder)
.GroupBy(x => GetReportName(Path.GetFileNameWithoutExtension(x))).Select(x => new ReportItem(x.Key, x.FirstOrDefault(), x.Skip(1).FirstOrDefault()));
But are you sure there will be exactly two items in each group? Maybe has it sence for ReportItem to accept IEnumerable, not just two strings?
I have the following code written to find common objects in a list of objects
https://dotnetfiddle.net/gCgNBf
..............................
var query = setOfPersons
.SelectMany(l => l.Select(l1 => l1))
.GroupBy(p => p.Id)
.Where(g => g.Count() == setOfPersons.Count);
After that, I need to convert "query" to a list of "Person" objects ( List ) to achieve something else.
I tried using "ToList()"... But it says:
" cannot convert IGrouping to a List ".
Can someone help me to fix it ?
Looking at your code it seems that what you are trying to achieve is to get the list of people that exist in each list. If so, you can use the following query:
var query = setOfPersons
.SelectMany(l => l.Select(l1 => l1))
.GroupBy(p => p.Id)
.Where(g => g.Count() == setOfPersons.Count)
.Select(x=>x.First()) // Select first person from the grouping - they all are identical
.ToList();
Console.WriteLine("These people appears in all set:");
foreach (var a in query)
{
Console.WriteLine("Id: {0} Name: {1}", a.Id, a.Name);
}
Here you select just a single item from each grouping, because they all are identical.
I have a collection of elements and some of these elements are duplicating. I need to extract all records but only the first record if the record is one of a duplicate set.
I was able to group the elements and find all elements that have duplicates, but how to remove every first element of a group?
var records =
dbContext.Competitors
.GroupBy(x => x.Email)
.Select(x => new { Properties = x,
Count = x.Key.Count() })
.Where(x => x.Count > 1)
.ToList();
EDIT: Seems like it's impossible to accomplish this task with EF, because it fails to translate the desired linq expression to SQL. I'll be happy if someone offer different approach.
To exclude the first record from each email-address group with more than one entry, you could do this:
var records = dbContext.Competitors
.GroupBy(x => x.Email)
.SelectMany(x => (x.Count() == 1) ? x : x.OrderBy(t=>t).Skip(1))
.ToList();
This is the logic :
Group by a property > Select every Group > (Possibly) Sort that > Skip first one
This can be turned into some linq code like this :
//use SelectMany to flat the array
var x = list.GroupBy(g => g.Key).Select(grp => grp.Skip(1)).SelectMany(i => i);
How can the below linq Query be modified such that i can get a Rounded figure of values.
var result=GetStudentsWithTheirMarks()
.OrderByDescending(x => Math.Round(x.PercentageScore)).Take(5)
.OrderBy(x => x.PercentageScore);
Please ignore the presence of two order by clause as this is done for with a purpose.
GetStudentsWithThierMarks returns Student List with their FirstName and PercentageScore.
I believe in the above query Math.Round is only applicable when during order by operation so final result still contains values in decimal places whereas i am only interested to see rounded figures with integer values. I just cant figure out the syntax.
You just need a Select :
var result= GetStudentsWithTheirMarks()
.OrderByDescending(x => Math.Round(x.PercentageScore))
.Take(5)
.OrderBy(x => x.PercentageScore)
.Select(x => Math.Round(x.PercentageScore));
You can store this value in an anonymous type:
var result = GetStudentsWithTheirMarks()
.Select(s => new
{
Student = s,
RoundedPercentageScore = Math.Round(s.PercentageScore)
})
.OrderByDescending(x => x.RoundedPercentageScore )
.Take(5)
.OrderBy(x => x.Student.PercentageScore);
Now you can access it in this way:
foreach(var x in result)
Console.WriteLine("RoundedPercentageScore: " x.RoundedPercentageScore);
I cannot seem to combine 2 GroupBy statements in 1 linq expression..
For now i'm doing something like this:
double maxInvestment = 0;
foreach (var playerAction in TotalUserActions.GroupBy(p => p.Player))
{
var MaxInvestmentPerPlayer = playerAction.GroupBy(p => p.RoundId)
.Select(p => p.LastOrDefault())
.Sum(p=> p.BetSize);
if(MaxInvestmentPerPlayer > maxInvestment)
maxInvestment = MaxInvestmentPerPlayer;
}
What I would like to do is something like this...
double maxInvestment = TotalUserActions.GroupBy(p => p.Player)
.GroupBy(p => p.RoundId)
.Select(p => p.LastOrDefault())
.Sum(p=> p.BetSize);
But that wont work.. Can someone help me on this?
Thanks!
Looks like this is what you want, the key takeaway being the inner query is wrapped in an outer call to Select():
var maxInvestment = TotalUserActions.GroupBy(p => p.Player)
.Select(g => g.GroupBy(x => x.RoundId)
.Select(x => x.LastOrDefault())
.Sum(x => x.BetSize))
.Max();
I do question your use of LastOrDefault() though as, since you have not specified any ordering, you may as well use FirstOrDefault() and save the hassle of skipping to the last element.