I have an Linq query like this:
var result = from c in displayedEmployees select new[] { c.Name, c.Code, c.Rank.ToString(), c.Id.ToString(),c.Rank. };
If i want to select the min and max of any column for example Rank along with this like:
var result = from c in displayedEmployees select new[] { c.Name, c.Code, c.Rank.ToString(), c.Id.ToString(),min(c.Rank) ,max(c.Rank)};
how can I do this?
Select actually performs a transformation of every item (displayedEmployee), so ends up with the same number of items as you started with. Min and max are reductions, they reduce the list into a scalar.
After the "select" keyword is a function that only recieves the current item (c in your case). So there is no way to get the max there and you don't want every item in result to repeat the same maximum value.
You should compute the minimum and maximum separately.
After:
var result = from c in displayedEmployees select { c.Name, c.Code, c.Rank };
You could do something like this:
var min = result.Min(x => x.Rank);
var max = result.Max(x => x.Rank);
See more samples here (LINQ 101): http://code.msdn.microsoft.com/101-LINQ-Samples-3fb9811b
Related
I am having trouble with a class that has a list of objects - basically it is a shopping cart where you can add items. I wish for the items to be grouped by the item id, so they would not appear more times in the cart.
So if you add an item, and then you add it again, it should appear as 1 row, quantity =2, instead of 2 rows quantity 1.
First of all, is there a way of automatically organizing a list this way?
If not, then I need another var:
var l = from i in list.cartItems
group i by i.id into g
select g.ToList();
list.cartItems = l;
list is the object, cartItems is the list, l would be the new list to "refresh"
However, this causes me an error:
Cannot implicitly convert type 'System.Collections.Generic.IEnumerable>' to 'System.Collections.Generic.List'. An explicit conversion exists (are you missing a cast?)
Any ideas?
Thanks
Edit:
I edited the error
Cartitems is just:
public List cartItems;
inside a CartItemList class
You should specify the grouped element you want, like this:
list.cartItems = l.First();
Your cartItems is a 'ListOfItems' type, and your var l is a new grouped type, which is 'int,ListOfItems' type. So to cast your 'int,ListOfItems' to cartItems which is 'ListOfItems', you should choose the element some element from your result collection.
for solve you need change select clause in your query - in select you can apply aggregate function like this:
var l = (from i in list.cartItems
group i by i.id into g
select new CartItem(){Id=g.Key, quantity=g.Count()}).ToList();
list.cartItems = l;
try sample that work
var t = Enumerable.Range(1, 10).Select(i => new { Id = i % 3, Q = 1 }).ToList();
var b = from i in t
group i by i.Id into g
select new { Id = g.Key, Q = g.Count() };
t = b.ToList();
and check your inputs
I am curious what the x is for in a a linq group by clause: group x by ...
The x can be replaced by an 1:
var query = from box in c.Boxes
join item in c.Items on box equals item.Box
group 1 by new { BoxId = box.BoxId, item.ItemType.ItemTypeId } into g
select new { g.Key.BoxId, g.Key.ItemTypeId, Count = g.Count() };
Does anybody have a sample where the x (or wathever local variable you chose in the group by ) is really of some value?
I mean
var query2 = from box in c.Boxes
group box by box.BoxId into q
select q.Key;
can be replaced by
var query2 = from box in c.Boxes
group 1 by box.BoxId into q
select q.Key;
That's the expression that determines what will go in the output of the group by clause.
You are actually not inspecting the whole output, but only the Keys, which are the same in the examples above, because the grouping is done by the same thing (box.BoxId).
However, replace the last line:
select q.Key;
with
select q;
You will notice that:
the group 1 by ... query will return an IGrouping<int, int> which will have all values set to 1
the group box by ... query will return an IGrouping<int, Box>, which will have all the boxId keys and, for each of them, the corresponding Box objects with respect to the grouping criteria.
In group x by... the x is what gets aggregated.
So you could write something like
var childrenByAge = from child in class
group getName(child) by child.Age;
This gives you a grouping containing names of children for each age.
Here is a simple example where you can test the difference easily:
static void Main(string[] args)
{
var grouping = from c in "Hello World!"
group c by c; // Replace 'group c by' with 'group 1 by'
// and compare results
foreach (var group in grouping)
{
Console.Write("KEY: {0} VALUES :", group.Key);
foreach (var value in group)
Console.Write(" {0}", value);
Console.WriteLine();
}
Console.ReadKey();
}
I'm trying to display cities names where a count is greater than 1. I can do it easy in SQL and am close in LINQ but can't figure out how to use group and also get a count and display a name
var query = (from c in Consumer
group c
by new { c.City, size = c.City.Count() }
into results
select new { Name = results.Key.City })
.Where(a => size > 0);
The size part doesn't work
try this query:
var list= Consumer.GroupBy(s=>s.City)
.Select(s=>new {
City = s.Key,
size = s.Count(),
})
.Where(s=>s.size>0).ToList();
I have divAssignments that has potential multiple rows by rNI, an official id, according to a compound key of Indictment and booking numbers.
rNI Booking Indictment
12345 954445 10 12345
12345 954445 10 12346
12345 954445 10 12347
So ID has a count of 3 for a single booking number for this rni.
I get lost attempting to generate a count and a group by booking Number:
var moreThen = from dA in divAssignments
select new { dA.rNI, IndictmentCount = dA.indictmentNumber.Count() };
Most of the examples are dealing with static int[] and don't seem to work in my case.
How do I get a group and then a count? If I could put in a having that would be fantastic.
from a t-sql POV I'd use this:
Select rni, bookingNumber, count(*) IndictmentCount
from divAssignments
group by rni, bookingNumber
having count(*) > 0
TIA
How about something like this:
var query = from item in divAssignments
group item by item.rNI into grouping
select new
{
Id = grouping.Key,
Count = grouping.Count()
}
If you're interested in grouping by both the rNI and the booking number, I would change it to this:
var query = from item in divAssignements
group item by new { item.rNI, a.Booking } into grouping
select new
{
Id = grouping.Key,
Count = grouping.Count
};
OR
var query = from item in divAssignments
group item by item into grouping
select new
{
Id = grouping.Key,
Count = grouping.Count()
}
and implement IEquatable on the divAssignment object to support equality comparison. The other option if you'd like is to write an IEqualityComparer instance to do the composite key comparison. Your query could then look like:
var query =
divAssignments
.GroupBy(i => i, new MyCustomEqualityComparer())
.Select(i => new { Key = i.Key, Count = i.Count());
var query =
from dA in divAssignments
group dA by new { dA.rNI, dA.bookingNumber };
foreach(var grp in query)
{
Console.WriteLine("rNI={0}, bookingNumber={1} => Count={2}", grp.Key.rNI, grp.Key.bookingNumber, grp.Count());
}
If you use a Grouping operator in Linq you will get what you need. The code:
var count = from a in divAssignments
group a by new { a.rNI, a.Booking } into b
select b;
will return a collection of IGrouping objects. This will give you the Key (in my example this will be an anonymous type with an rNI and a Booking property) and a collection of the divAssignments that match the key.
Using Method syntax (much easier to read in my opinion):
First group the records, then select a new result for each group that contains the count.
var groups = divAssignments.GroupBy(d => new { d.rNI, d.Booking });
groups.Select(g=> new { g.Key.rNI, g.Key.Booking, IndictmentCount = g.Count() });
I have the following LINQ conditional where clause query that produces a result of weights:
From this, I'd like to take the result set and join on another table, tblPurchases
var result = weights.Join(getsuppliersproducts.tblPurchases,
w => new { w.MemberId, w.MemberName, w.LocationId, w.UnitId },
p => new { p.MemberId, p.MemberName, p.LocationId, p.UnitId },
(w, p) => p);
In this second table, I have two columns I would like to perform an aggreagte function on, a sum on PurchaseQuantity and a count of UnitID.
So in its raw format, tblPurchases would look like so:
MemberID LocationID UnitId SupplierID SupplierStatus Purchases
1 1 ab Sup1 Live 10
1 1 abc Sup1 Live 10
1 1 abcd Sup2 Dead 50
From my results data set, I would like the output to look like so:
MemberID LocationID SupplierID SupplierStatus UnitIdCount Total Purchases
1 1 Sup1 Live 2 50
Also, with these amendments, can I still return this to a List?
How do I implement this using LINQ? I have tried, and failed miserably.
(To those who have seen my previous posts, I'm trying to cover all angles so I can fully understand the concept of what is going on in both SQL and LINQ)
That query will return an IEnumerable where each of the Purchases matches the MemberId, MemberName, LocationId and UnitId in the original Weights query. You can only easily do one aggregate at a time, so
var result = weights.Join(getsuppliersproducts.tblPurchases,
w => new { w.MemberId, w.MemberName, w.LocationId, w.UnitId },
p => new { p.MemberId, p.MemberName, p.LocationId, p.UnitId },
(w, p) => p).ToList();
Int32 count = result.Count();
Double quantity = result.Sum(p => p.PurchaseQuantity);
Is that what you're trying to do?
EDIT, after your reply of I would like to reutrn a list of tblPurchases with two new columns, the sum of Purchase Quantity and count of unit ID.
This gives a flat output:
var query = Weights.GroupJoin(
Purchases,
w => new {w.MemberId, w.LocationId},
p => new {p.MemberId, p.LocationId},
(w,p) => new {w.MemberId, w.LocationId, Count = p.Count(), Sum = p.Sum(x => x.Purchases)} );
Note that at the point we do the (w, p) => new {} that w is a single Weight and p is a list of Purchases matching that weight, so you can still keep all of teh (hierarchical) data:
var query = Weights.GroupJoin(
Purchases,
w => new {w.MemberId, w.LocationId},
p => new {p.MemberId, p.LocationId},
(w,p) => new {w.MemberId, w.LocationId, Count = p.Count(), Sum = p.Sum(x => x.Purchases), Purchases = p} );