I am having a struct as
public struct structMailJob
{
public string ID;
public string MailID;
public int ResendCount;
public int PageCount;
}
and a list as
List<structMailJob> myStructList = new List<structMailJob>();
I have loaded data in myStructList from database and want myStructList data in a new list after grouping by MailID and ResendCount.
I am trying as:
List<structMailJob> newStructList = new List<structMailJob>();
newStructList = myStructList.GroupBy(u => u.MailID, u=>u.ResendCount)
.Select(grp => new { myStructList = grp.ToList() })
.ToList();
but unable to do that as getting error message - cant implicitly convert generic list to structMailJob.
I think that you are looking for is the following:
var newStructList = myStructList.GroupBy(smj => new { smj.MailID, smj.ResendCount })
.Select(grp => new
{
MailID = grp.Key.MailID,
ResendCount = grp.Key.ResendCount
MailJobs = grp.Select(x=>new
{
x.ID,
x.PageCount
}).ToList()
})
.ToList();
Note that we changed the GroupBy clause to the following one:
GroupBy(smj => new { smj.MailID, smj.ResendCount })
Doing so, the key on which the groups would be created would be consisted of both MailID and ResendCount. By the way the former GroupBy clause isn't correct.
Then having done the grouping, we project each group to an object with three properties, MailID and ResendCout, which are the components of the key and list of anonymous type object with two properties, ID and PageCount, which we gave it the name MailJobs.
Last but not least you will notice that I didn't mention the following
List<structMailJob> newStructList = new List<structMailJob>();
I just used the var and declared the newStructList. I don't think that you stated in your post makes sense. How do we expect to get a list of the same objects after grouping them? So I assumed that you might want is the above.
However, I thought you might want also something like this and you didn't want to refer to Grouping.
myStructList = myStructList.OrderBy(smj => smj.MailID)
.ThenBy(smj => smj.ResendCount)
.ToList();
Linq Query is completely incorrect, following are the important points:
myStructList.GroupBy(u => u.MailID, u=>u.ResendCount) // Incorrect grouping
myStructList.GroupBy(u => new {u.MailID, u.ResendCount }) // Correct grouping, which will do by two columns MailID and ResendCount, last one was only doing by MailID and was using ResendCount for result projection
Now the result is of type IEnumerable<IGrouping<AnonymousType,structMailJob>>, so when you do something like Select, it will end up creating Concatenated List of type IEnumerable<List<structMailJob>> (Removed the assignment to myStructList inside the Select, as that was not correct):
.Select(grp => grp.ToList())
Correct code would require you to flatten using SelectMany as follows:
newStructList = myStructList.GroupBy(u => new {u.MailID, u.ResendCount})
.SelectMany(grp => grp.ToList()).ToList();
Assign it to newStructList, but this code has little use, since literally newStructList is exactly same as myStructList post flattening, ideally you shall be able to use the grouping, so that you can get a subset and thus the correct result, however that depends on your business logic
I don't know if I got your question right but it seems to me you missed the 'Group by' signature.
List<structMailJob> myStructList = new List<structMailJob>();
List<structMailJob> newStructList = new List<structMailJob>();
newStructList = myStructList
// .GroupBy(/*Key Selector */u => u.MailID, /*Element Selector*/u=>u.ResendCount)
.GroupBy(u => new { u.MailID, u.ResendCount }) // broup by MailID, ResendCount
// Note no Element Selector , the 'STRUCT' is 'SELECTED'
.Select(grp => {
// NOte: Key == Anonymous {MailID, ResendCount }
return grp;
})
// otherwise you get a IEnumerable<IEnumerable<T>> instead of IEnumerable<T> because you grouped it
.SelectMany(x=>x)
.ToList();
If Mrinal Kamboj's answer is what you are looking for, then you could use the following as an alternative:
var orderedList = myStructList.OrderBy(x => x.MailID).ThenBy(x => x.ResendCount);
Related
List<MyObject> objects = await item.tables.ToAsyncEnumerable()
.Where(p => p.field1 == value)
.Select(p => new MyObject(p.field1,p.field2))
.ToList();
^ I have something like that, but what i'm wondering, is there anyway way to add a second object creation, in the same select? eg. new MyObject(p.field3,p.field4) ? and add it to the same list? order does not matter.
I know could do this with multiple calls to database or splitting up lists into sections, but is there way to do this in single line?
You could create it as a tuple.
List<Tuple<MyObject1, MyObject2>> = query.Select(x => Tuple.Create(
new MyObject1
{
// fields
},
new MyObject2
{
//fields
}))
.ToList();
From my testing in Linqpad, it seems that this will only hit the database once.
Alternatively, you could just select all the fields you know you'll need from the database to create both:
var myList = query.Select(x => new { FieldA = x.FieldA, FieldB = x.FieldB }).ToList(); //hits db once
var object1s = myList.Select(x => new MyObject1(x.FieldA));
var object2s = myList.Select(x => new MyObject1(x.FieldB));
var bothLists = object1s.Concat(object2s).ToList();
What you'd want to do is use the SelectMany method in linq. Which will select all the items from an array. The array can be created anonymously as seen below.
List<MyObject> objects = await item.tables.ToAsyncEnumerable()
.Where(p => p.field1 == value)
.SelectMany(p => new []{new MyObject(p.field1,p.field2), new MyObject(p.field3,p.field4)})
.ToList();
Hope that solves you problem!
If you use query syntax instead of method chaining, you can use the let operator to accomplish this. Note that the SQL generated may not be exactly performant as this article shows, but it should work for you if you're after a subquery.
You could try creating an array of objects and then flattening with SelectMany:
List<MyObject> objects = await item.tables.ToAsyncEnumerable()
.Where(p => p.field1 == value)
.Select(p => new [] {
new MyObject(p.field1,p.field2),
new MyObject(p.field3,p.field4)
})
.SelectMany(g => g)
.ToList();
But I suspect you'll have problems getting EF to translate that to a query.
Edit: Code works fine, it was an other bug.
I had comment out the //department.IdAgency = reader.GetByte(2); line, in the created departmentList. When I removed the // then the IQueryable<string> with .Where works fine. Sorry for the inconvenience!
static List<Department> CreateDepartmentList(IDataReader reader)
{
List<Department> departmentList = new List<Department>();
Department department = null;
while (reader.Read())
{
department = new Department();
department.Id = reader.GetByte(0);
department.Name = reader.GetString(1);
//department.IdAgency = reader.GetByte(2);
if (!reader.IsDBNull(3))
{ department.IdTalkGroup = reader.GetInt16(3); }
departmentList.Add(department);
}
return departmentList;
}
Original question:
I have an IQueryable<string> query, that works. But how do I use .Where?
IQueryable<string> query = departmentList.AsQueryable()
.OrderBy(x => x.Name)
.Select(x => x.Name);
I have tried this, but it does not work:
IQueryable<string> query = departmentList.AsQueryable()
.OrderBy(x => x.Name)
.Where(x => x.IdAgency == idAgencySelected[0])
.Select(x => x.Name);
All the .Where() call does is apply a filtering method to each element on the list, thus returning a new IEnumerable.
So, for some IQueryable<string>...
IEnumerable<string> results = SomeStringList.Where(s => s.Contains("Department"));
...You would get a list of strings that contain the word department.
In other words, by passing it some boolean condition that can be applied to a member of the queryable collection, you get a subset of the original collection.
The reason your second block of code does not work, is because you're calling a method or property that does not belong to string. You may want to consider querying against the more complex type, if it has identifier data, and then take the names of the elements and add them to some list instead.
How can I turn the following statement back to List<DocumentData>
IEnumerable<IGrouping<string, DocumentData>> documents =
documentCollection.Select(d => d).GroupBy(g => g.FileName);
the goal is to get List that should be smaller than documentCollection.
FileName contains duplicates so I want to make sure I don't have duplicate names.
I have also tried the following but it's still providing me with duplicate file names
documentCollection =
documentCollection.GroupBy(g => g.FileName).SelectMany(d => d).ToList();
Each IGrouping<string, DocumentData> is an IEnumerable<DocumentData>, so you could simply call SelectMany to flatten the sequences:
var list = documents.SelectMany(d => d).ToList();
Edit: Per the updated question, it seems like the OP wants to select just the first document for any given filename. This can be achieved by calling First() on each IGrouping<string, DocumentData> instance:
IEnumerable<DocumentData> documents =
documentCollection.GroupBy(g => g.FileName, StringComparer.OrdinalIgnoreCase)
.Select(g => g.First())
.ToList();
You haven't said what T should stand for in List<T> you're looking for, so here are couple the most likely to be desired:
List<DocumentData> - rather pointless as you already have that on documentCollection
var results = documents.SelectMany(g => g).ToList();
List<KeyValuePair<string, List<DocumentData>>
var results =
documents.Select(g => new KeyValuePair(g.Key, g.ToList())).ToList();
List<string> - just the names
var results = documents.Select(g => g.Key).ToList();
List<IGrouping<string, DocumentData>>
var results = documents.ToList();
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) };
SFC.OrderFormModifiedMonitoringRecords
.SelectMany(q => q.TimeModify, w => w.DateModify)
.Distinct()
.OrderBy(t => t)
.SelectMany(t => new { RowID = t.rowID, OFnum = t.OFNo });
It's Error did i missed something or is it Completely Coded The Wrong Way? After this i'm gonna use this on a Foreach method to gather up multiple data without the duplicates.
The delegate you pass to SelectMany must return an IEnumerable and is for collapsing multiple collections into one. So yes, something's definitely wrong here. I think you've confused it with Select which simply maps one collection to another.
Without knowing what your goal is, it's hard to know exactly how to fix it, but I'm guessing you want something like this:
SFC.OrderFormModifiedMonitoringRecords
.OrderBy(t => t.DateModify)
.ThenBy(t => t.TimeModify)
.Select(t => new { RowID = t.rowID, OFnum = t.OFNo })
.Distinct();
Or in query syntax:
(from t in SFC.OrderFormModifiedMonitoringRecords
orderby t.DateModify, t.TimeModify
select new { RowID = t.rowID, OFnum = t.OFNo })
.Distinct();
This will order the records by DateModify then by TimeModify, select two properties, rowID and OFNo and return only distinct pairs of values.