I have a linq query which is almost complete.
It's working but I need to retrieve the original list of the items in the list that fulfills the requirements.
Now it only returns true or false if any has the count > numberOfResourceToBook.
But instead I want to return all the items in availableTimes having that (with all its properties).
bool enoughResourceAvailable = availableTimes.GroupBy(l => new { l.From, l.To })
.Select(g => new
{
Date = g.Key,
Count = g.Select(l => l.ResourceId).Distinct().Count()
}).Where(c => c.Count >= numberOfResourcesToBook).Count() > 0;
I realize this is an old question and hopefully you already figured this out long ago. But for someone else stumbling into this question, here is how you could solve it:
First, you need to add the available times for each group to the anonymous objects you are selecting so you have a way to get them back after grouping. Get rid of the .Count > 0 at the end so the result is an IEnumerable of the anonymous objects instead of a boolean.
var result = availableTimes
.GroupBy(l => new { l.From, l.To })
.Select(g => new
{
Date = g.Key,
Count = g.Select(l => l.ResourceId).Distinct().Count(),
Times = g.Select(l => l) // Add this to capture the times for the group
})
.Where(c => c.Count >= numberOfResourcesToBook);
Next, you can set the enoughResourceAvailable by using .Any() on the previous result. It does the same job as .Count() > 0 except it doesn't always need to enumerate the entire list: it can return true as soon as it finds at least one item.
bool enoughResourceAvailable = result.Any();
Lastly, to get all the times back which matched the query (if there are any), you can use SelectMany() on the result, like so:
var allMatchingTimes = result.SelectMany(c => c.Times);
Working demo: https://dotnetfiddle.net/HCEuMR
Related
I have a simple class:
class Balls
{
public int BallType;
}
And i have a really simple list:
var balls = new List<Balls>()
{
new Balls() { BallType = 1},
new Balls() { BallType = 1},
new Balls() { BallType = 1},
new Balls() { BallType = 2}
};
I've used GroupBy on this list and I want to get back the key which has the highest count/amount:
After I used x.GroupBy(q => q.BallType) I tried to use .Max(), but it returns 3 and I need the key which is 1.
I also tried to use Console.WriteLine(x.GroupBy(q => q.Balltype).Max().Key); but it throws System.ArgumentException.
Here's what I came up with:
var mostCommonBallType = balls
.GroupBy(k => k.BallType)
.OrderBy(g => g.Count())
.Last().Key
You group by the BallType, order by the count of items in the group, get the last value (since order by is in an ascending order, the most common value would be the last) and then return it's key
Some came up with the idea to order the sequence:
var mostCommonBallType = balls
.GroupBy(k => k.BallType)
.OrderBy(g => g.Count())
.Last().Key
Apart from that it is more efficient to OrderByDescending and then take the FirstOrDefault, you also get in trouble if your collection of Balls is empty.
If you use a different overload of GroupBy, you won't have these problems
var mostCommonBallType = balls.GroupBy(
// KeySelector:
k => k.BallType,
// ResultSelector:
(ballType, ballsWithThisBallType) => new
{
BallType = ballType,
Count = ballsWithThisBallType.Count(),
})
.OrderByDescending(group => group.Count)
.Select(group => group.BallType)
.FirstOrDefault();
This solves the previously mentioned problems. However, if you only need the 1st element, why would you order the 2nd and the 3rd element? Using Aggregate instead of OrderByDescending will enumerate only once:
Assuming your collection is not empty:
var result = ... GroupBy(...)
.Aggregate( (groupWithHighestBallCount, nextGroup) =>
(groupWithHighestBallCount.Count >= nextGroup.Count) ?
groupWithHighestBallCount : nextGroup)
.Select(...).FirstOrDefault();
Aggregate takes the first element of your non-empty sequence, and assigns it to groupWithHighestBallCount. Then it iterates over the rest of the sequence, and compare this nextGroup.Count with the groupWithHighestBallCount.Count. It keeps the one with the hightes value as the next groupWithHighestBallCount. The return value is the final groupWithHighestBallCount.
See that Aggregate only enumerates once?
First, sorry for a bad title, I don't really know what this is called.
I know that I can use context.Model.Where(a => a.Entity == "example").Count(). But I want something more generic where I can get a count of how many rows have the same entry in one of the columns. A pic of what I mean:
My end result that I wanna get is a list of the count like: 3, 1 etc
You can use a GroupBy statement for this to group by a value of your items, and then Select the result you want from it:
var result = await db.Model
.GroupBy(x => x.Age)
.Select(g => new {
Age = g.Key,
Count = g.Count(),
})
.ToListAsync();
The result is a list of objects that have an Age property with the age value, and a Count property with the number of items that had that Age value.
If you just want the counts, then you can just return those from the Select expression directly:
var result = await db.Model
.GroupBy(x => x.Age)
.Select(g => g.Count())
.ToListAsync();
Note that this will obviously prevent you from saying what age an individual count is representing.
Try using the distinct method and get as anonymous object then applying count on it
context.Model.Where(a => a.Entity == "example").Select(a = > new {a.User, a.Address, a.Age}).Distinct().Count()
I want to access the first, second, third elements in a list. I can use built in .First() method for accessing first element.
My code is as follows:
Dictionary<int, Tuple<int, int>> pList = new Dictionary<int, Tuple<int, int>>();
var categoryGroups = pList.Values.GroupBy(t => t.Item1);
var highestCount = categoryGroups
.OrderByDescending(g => g.Count())
.Select(g => new { Category = g.Key, Count = g.Count() })
.First();
var 2ndHighestCount = categoryGroups
.OrderByDescending(g => g.Count())
.Select(g => new { Category = g.Key, Count = g.Count() })
.GetNth(1);
var 3rdHighestCount = categoryGroups
.OrderByDescending(g => g.Count())
.Select(g => new { Category = g.Key, Count = g.Count() })
.GetNth(2);
twObjClus.WriteLine("--------------------Cluster Label------------------");
twObjClus.WriteLine("\n");
twObjClus.WriteLine("Category:{0} Count:{1}",
highestCount.Category, highestCount.Count);
twObjClus.WriteLine("\n");
twObjClus.WriteLine("Category:{0} Count:{1}",
2ndHighestCount.Category, 2ndHighestCount.Count);
// Error here i.e. "Can't use 2ndHighestCount.Category here"
twObjClus.WriteLine("\n");
twObjClus.WriteLine("Category:{0} Count:{1}",
3rdHighestCount.Category, 3rdHighestCount.Count);
// Error here i.e. "Can't use 3rdHighestCount.Category here"
twObjClus.WriteLine("\n");
I have written extension method GetNth() as:
public static IEnumerable<T> GetNth<T>(this IEnumerable<T> list, int n)
{
if (n < 0)
throw new ArgumentOutOfRangeException("n");
if (n > 0){
int c = 0;
foreach (var e in list){
if (c % n == 0)
yield return e;
c++;
}
}
}
Can I write extension methods as .Second(), .Third() similar to
built in method .First() to access second and third indices?
If what you're looking for is a single object, you don't need to write it yourself, because a built-in method for that already exists.
foo.ElementAt(1)
will get you the second element, etc. It works similarly to First and returns a single object.
Your GetNth method seems to be returning every Nth element, instead of just the element at index N. I'm assuming that's not what you want since you said you wanted something similar to First.
Since #Eser gave up and doesn't want to post the correct way as an answer, here goes:
You should rather do the transforms once, collect the results into an array, and then get the three elements from that. The way you're doing it right now results in code duplication as well as grouping and ordering being done multiple times, which is inefficient.
var highestCounts = pList.Values
.GroupBy(t => t.Item1)
.OrderByDescending(g => g.Count())
.Select(g => new { Category = g.Key, Count = g.Count() })
.Take(3)
.ToArray();
// highestCounts[0] is the first count
// highestCounts[1] is the second
// highestCounts[2] is the third
// make sure to handle cases where there are less than 3 items!
As an FYI, if you some day need just the Nth value and not the top three, you can use .ElementAt to access values at an arbitrary index.
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);
This question already has answers here:
List sort based on another list
(3 answers)
Closed 9 years ago.
I am building a search function which needs to return a list ordered by relevance.
IList<ProjectDTO> projects = new List<ProjectDTO>();
projects = GetSomeProjects();
List<ProjectDTO> rawSearchResults = new List<ProjectDTO>();
//<snip> - do the various search functions here and write to the rawSearchResults
//now take the raw list of projects and group them into project number and
//number of search returns.
//we will sort by number of search returns and then last updated date
var orderedProjects = rawSearchResults.GroupBy(x => x.ProjectNbr)
.Select(x => new
{
Count = x.Count(),
ProjectNbr = x.Key,
LastUpdated = x.First().UpdatedDateTime
})
.OrderByDescending(x => x.Count)
.ThenByDescending(x => x.LastUpdated);
So far so good; the "orderedProjects" variable returns my list in the correct order. However, I need the entire object for the next step. When I try to query back to get the original object type, my results lose their order. In retrospect, this makes sense, but I need to find a way around it.
projects = (from p in projects
where orderedProjects.Any(o => o.ProjectNbr == p.ProjectNbr)
select p).ToList();
Is there a LINQ-friendly method for preserving the order in the above projects query?
I can loop through the orderedProject list and get each item, but that's not very efficient. I can also rebuild the entire object in the original orderedProjects query, but I'd like to avoid that if possible.
You need to do it the other way around:
Query orderedProjects and select the corresponding items from projects:
var projects =
orderedProjects
.Select(o => projects.SingleOrDefault(p => p.ProjectNbr == o.ProjectNbr))
.Where(x => x != null) // This is only necessary if there can be
// ProjectNbrs in orderedProjects that are not in
// projects
.ToList();
You shouldn't use "Select" in the middle there as that operator transforms the object into another type and you say that you need the original object.
var orderedProjects = rawSearchResults.GroupBy(x => x.ProjectNbr)
.OrderByDescending(x => x.Count)
.ThenByDescending(x => x.First().UpdatedDateTime);
Do they come in chronological order or something? Otherwise, I'm pretty sure you want the "ThenByDescending" to be performed on the newest or oldest project update like so:
var orderedProjects = rawSearchResults.GroupBy(x => x.ProjectNbr)
.OrderByDescending(x => x.Count)
.ThenByDescending(x => x.Max(p=>p.UpdatedDateTime));