We Keep Coding

Grouping and sum

I have a list as follows which will contain the following poco class.
public class BoxReportView
{
public DateTime ProductionPlanWeekStarting { get; set; }
public DateTime ProductionPlanWeekEnding { get; set; }
public string BatchNumber { get; set; }
public string BoxRef { get; set; }
public string BoxName { get; set; }
public decimal Qty { get; set; }
public FUEL_KitItem KitItem { get; set; }
public decimal Multiplier { get; set; }
}
I am wanting to group the report and sum it by using the BoxName and also the Qty SO I tried the following
var results = from line in kitItemsToGroup
group line by line.BoxName into g
select new BoxReportView
{
BoxRef = g.First().BoxRef,
BoxName = g.First().BoxName,
Qty = g.Count()
};
In My old report I was just doing this
var multiplier = finishedItem.SOPOrderReturnLine.LineQuantity -
finishedItem.SOPOrderReturnLine.StockUnitDespatchReceiptQuantity;
foreach (KitItem kItem in kitItems.Cast<KitItem().Where(z => z.IsBox == true).ToList())
{
kittItemsToGroup.Add(new BoxReportView() {
BatchNumber = _batchNumber,
ProductionPlanWeekEnding = _weekEndDate,
ProductionPlanWeekStarting = _weekStartDate,
BoxRef = kItem.StockCode,
KitItem = kItem,
Multiplier = multiplier,
Qty = kItem.Qty });
}
}
Then I was just returning
return kitItemsToGroup;
But as I am using it as a var I cannot what is best way to handle the grouping and the sum by box name and qty.

Whether it is the best way depends upon your priorities. Is processing speed important, or is it more important that the code is easy to understand, easy to test, easy to change and easy to debug?
One of the advantages of LINQ is, that it tries to avoid enumeration of the source more than necessary.
Are you sure that the users of this code will always need the complete collection? Can it be, that now, or in near future, someone only wants the first element? Or decides to stop enumeration after he fetched the 20th element and saw that there was nothing of interest for him?
When using LINQ, try to return IEnumerable<...> as long as possible. Let only the end-user who will interpret your LINQed data decide whether he wants to take only the FirstOrDefault(), or Count() everything, or put it in a Dictionary, or whatever. It is a waste of processing power to create a List if it is not going to be used as a List.
your LINQ code and your foreach do some completely different things. Alas it is quite common here on StackOverflow for people to ask for LINQ statements without really specifying their requirements. So I'll have to guess something in between your LINQ statement and your foreach.
Requirement Group the input sequence of kitItems, which are expected to be Fuel_KitItems into groups of BoxReportViews with the same BoxName, and select several properties from every Fuel_KitItem in each group.
var kitItemGroups = kitItems
.Cast<Fuel_KitItem>() // only needed if kitItems is not IEnumerable<Fuel_KitItem>
// make groups of Fuel_KitItems with same BoxName:
.GroupBy(fuelKitItem => fuelKitItem.BoxName,
// ResultSelector, take the BoxName and all fuelKitItems with this BoxName:
(boxName, fuelKitItemsWithThisBoxName) => new
{
// Select only the properties you plan to use:
BoxName = boxName,
FuelKitItems = fuelKitItemsWithThisBoxName.Select(fuelKitItem => new
{
// Only Select the properties that you plan to use
BatchNumber = fuelKitItem.BatchNumber,
Qty = fuelKitItem.Qty,
...
// Not needed, they are all equal to boxName:
// BoxName = fuelKitItem.BoxName
})
// only do ToList if you are certain that the user of the result
// will need the complete list of fuelKitItems in this group
.ToList(),
});
Usage:
var kitItemGroups = ...
// I only need the KitItemGroups with a BoxName starting with "A"
var result1 = kitItemGroups.Where(group => group.BoxName.StartsWith("A"))
.ToList();
// Or I only want the first three after sorting by group size
var result2 = kitItemGroups.OrderBy(group => group.FuelKitItems.Count())
.Take(3)
.ToList();
Efficiency Improvements: As long as you don't know how your LINQ will be used, don't make it a List. If you know that chances are high that the Count of group.FuelKitItems is needed, to a ToList

Linq to Collection - Dynamic Where Clause

I have a WPF applicaion of which i would like to populate a treeview. Before this happens I would like the user to be able to select any of the fields/properties available in the collection from a drop down that will then populate the tree with data and grouped appropriately.
EXAMPLE Object
public class class_01{
public string Property_A {get; set;}
public string Property_B {get; set;}
public string Property_C {get; set;}
}
EXAMPLE Collection
List<class_01> list_01 = new List<class_01>();
Again, the drop down will be bound with what ever properties are available from the list. This way if the list where to change the application would not require modification. This is a big requirement for the answer i need.
Lets say the user selects "Property_A".
I would like a linq query method that looks something like this.
Linq Query
public groupingModel getGrouping(string groupBy) // groupby equals property A in this example
{
List<class_01> list = getList(); //Returns the list of data of type class_01
var q = from x in w where ????? == groupBy select x; // I dont want to specify a specific property but rather have one applied dynamically
return q;
}
I have a custom object that the query would then be parsed into. that looks similar to the following.
Custom Object
public class class_02{
public string header {get; set;} // will be set to the discrete values of the selected groupby property
public List<class_01> prop_a {get; set;}
}
This would then be bound to the tree appropriately.
Any Thoughts?
EDIT
Additionally how would I get a list of the unique value for the property the user selects.
for example
{a = 1, b =2, c =3}, {a = 2, b = 3, c = 4}
if the user decides to group on property "a" how would we produce a collection of [1,2]?
This will be needed to construct a where clause.
foreach(value of user selected property){
string whereClause = string.format("{0} = {1}",selected property, value")
}
EDIT - Catching exception from Dynamic Query
public List<groupingModel> getGrouping(string groupBy)
{
List<groupingModel> lgm = new List<groupingModel>();
//Categories.Select(c => c.Id).ToList()
var w2 = getWVWellsList();
//var v = w2.Select(groupBy).Distinct().Cast<string>().ToArray();
var v = w2.Select(groupBy).Distinct();
foreach(string val in v)
{
string whereClause = string.Format("{0} = {1}", groupBy, val);
try
{
IEnumerable<WVWellModel> q2 = w2.Where(whereClause);
List<WVWellModel> l = q2.ToList<WVWellModel>();
lgm.Add(new groupingModel { Header = val, Wells = l });
}
catch (Exception e)
{
MessageBox.Show(e.Message, "Query Error", MessageBoxButton.OK, MessageBoxImage.Error);
throw new Exception("Generic Exception - Issue With Group By Query", e);
}
}
return lgm;
}
Exception
"No Property or field "Colorado" Exists in type WVWellModel"
In the case of this example i can confirm that my where clause was "State = Colorado". It appears the query is applying the value as opposed to the property state which is apart of that type. It is as if it is reversed when the query is called.

Check at the post of Scott Gu
https://weblogs.asp.net/scottgu/dynamic-linq-part-1-using-the-linq-dynamic-query-library

Given a list of several of the same object, group and combine them based on field value

Sorry for the incoherent title. I don't know how to concisely explain my problem, which is why I didn't really know how to look it up. I'll explain using an example...
Let's say I have a class:
public class cas
{
public string name { get; set; }
public int num { get; set; }
}
With that class, I make several objects and stick them into a list. For the sake of example, I will make 4:
var list = new List<cas>
{
new cas { name = "firstname", num = 1 },
new cas { name = "firstname", num = 2 },
new cas { name = "lastname", num = 3 },
new cas { name = "lastname", num = 4 }
};
Is there a way to take this List and combine any objects with the same name field?
So, the new list would be 1 object with:
name = "firstname", num = 3,
name = "lastname", num = 7
There's the obvious "long" way to do it, but it would be clunky and expensive (go through the list several times to find like-objects). I was wondering if I was missing any clean way of doing it. I intentionally made a simple example so that the answer would be a proof of concept rather than writing my code for me. My actual problem is more complex than this, but I can't figure out this one aspect of it.

Using Linq, you have a GroupBy Method and a Select Method:
list = list.GroupBy(x=> x.name)
.Select(x=> new cas() { name = x.Key, num = x.Sum(y=> y.num) }).ToList();
Or using Elegant query-syntax:
list = (from item in list
group item by item.name into grouping
select new cas()
{
name = grouping.Key,
num = grouping.Sum(x => x.num)
}).ToList();
Note that to use these methods, you have to add using System.Linq at the top of your source file.

You can use linq, you would have to group them on name property and then sum on the num property of each group like:
var result = list.GroupBy(x=>x.name)
.Select(g=> new cas
{
name = g.Key,
num = g.Sum(x=>x.num)
});

List<object> Self-Filter

I have a list like
List<VoieData> listVoieData = new List<VoieData>();
and in VoieData Class I have :
public class VoieData
{
public int Depart { set; get; }
public int Arrive { set; get; }
public int DistanceDepart { set; get; }
public int DistanceArrive { set; get; }
}
Since I have a massive values I want to only consider all my Depart number , I would like to filter the listVoieData by finding the Arrive only have the same value as the
Depart
for example I have
listVoieData.Select(p=>p.Depart).ToList()= List<int>{1,2,3};
listVoieData.Select(p=>p.Arrive).ToList()= List<int>{1,2,3,4,5};
I need to throw away the entire VoieData which contain {4,5} as Arrive
right now my soulution is like this , but it' s not correct ;
List<VoieData> listVoieDataFilter = listVoieData .Join(listVoieData , o1 => o1.Arrive, o2 => o2.Depart, (o1, o2) => o1).ToList();
Sorry for the confusing question ;
I want to remove Arrive which is different from all the Depart in the list list , and return the new
List
it 's not only in one VoieData;
Arrive!=Depart
Thanks

I think you want to remove all objects where Arrive is not in any of the Depart from any object. In that case, first get all Depart and then filter by Arrive:
HashSet<int> allDepart = new HashSet<int>(listVoieData.Select(x => x.Depart));
var result = listVoieData.Where(v => !allDepart.Contains(v.Arrive))
We use a HashSet<int> for efficiency.

Use LINQ Where:
var records = listVoieData.Where(x => x.Arrive == x.Depart);
This will return results where both Arrive and Depart are the same.

That would be a typical case to use linq.
something like:
var res = from data in listVoieData
where data.Depart == data.Arrive
select data;
and then optionally just use res.ToArray() to run the query and get the array.

Since you've stated that you want:
I want to remove Arrive which is different from all the Depart
This can be re-phrased as, "The set of all arrivals except those in the set of departures", which translates very nicely into the following LINQ query:
var arrivalsWithNoDepartures = listVoieData.Select(p=>p.Arrive)
.Except(listVoieData.Select(p=>p.Depart));

Entity Framework LINQ projection into custom type results in missing data

I have a many to many relationship between Contractors and SafetyCouncils. They are joined by a bridge table ContractorsSafetyCouncils which consists of ContractorId and SafetyCouncilId. These 2 columns form a composite key. This relationship is mapped correctly in EF4. The Contractor entity has the property:
public virtual ICollection<SafetyCouncil> SafetyCouncils
{
get;
set;
}
And the SafetyCouncil entity has the property:
public virtual ICollection<Contractor> Contractors
{
get;
set;
}
When accessing these properties via lazy loading from a single Contractor or SafetyCouncil entity, they work exactly as expected. But when accessing this relationship in a query:
from c in ContractorRepository.All()
where c.PQFs.Count() > 0
let psmAudits = c.PQFs.SelectMany(pqf => pqf.Audits)
let psmAudit = psmAudits.FirstOrDefault(audit => audit.CompletedDate == psmAudits.Max(a => a.CompletedDate))
let scsAudits = c.PQFs.SelectMany(pqf => pqf.SCSAudits)
let scsAudit = scsAudits.FirstOrDefault(audit => audit.CompletedDate == scsAudits.Max(a => a.CompletedDate))
select new MasterListItem()
{
AdministratorNotes = c.AdminFlags.Where(f => f.IsActive && f.ForPQF).Select(f => f.Text),
CanViewInfo = false,
ContractorName = c.ContractorName,
ContractorId = c.Id,
ContractorTaxId = c.TaxId,
SafetyCouncilIds = c.SafetyCouncils.Select(sc => sc.Id),
PQFSubmitted = c.PQFs.Max(p => p.PQFInfo.SubmittedDate.Value),
PSMAuditId = psmAudit.Id,
PSMAuditComplete = psmAudit.CompletedDate,
PSMAuditStatus = psmAudit.Status.Description,
SCSAuditId = scsAudit.Id,
SCSAuditComplete = scsAudit.CompletedDate
};
The problem occurs with:
SafetyCouncilIds = c.SafetyCouncils.Select(sc => sc.Id),
For every record the SafetyCouncilIds collection has 0 members, when based on the data in the database every record should have at least 1 SafetyCouncilId associated with it.
If I run the same query, but project into an anonymous type instead of the MasterListItem type, it works correctly. Why can't I project this query into my custom type?
Update:
My MasterListItem POCO contained the following properties:
public string SafetyCouncilIdsString
{
get;
set;
}
public IEnumerable<int> SafetyCouncilIds
{
set
{
StringBuilder sb = new StringBuilder(",");
foreach (var id in value)
{
sb.Append(id);
sb.Append(",");
}
this.SafetyCouncilIdsString = sb.ToString();
}
}
The SafetyCouncilIds property was the cause of the problem. I changed this to an automatic property and built the string elsewhere and projecting onto the POCO worked like a charm.

public IEnumerable<int> SafetyCouncilIds
{
set
{
StringBuilder sb = new StringBuilder(",");
foreach (var id in value)
{
sb = sb.Append(id).Append(","); // <-- try this
// *or sb = sb.AppendFormat("{0},", id);*
}
this.SafetyCouncilIdsString = sb.ToString();
}
}

I have two suggestions:
Try to isolate the the problem by removing any extra parts of the query.
Compare the two sql queries generated and find the differences.
Unfortunately, without access to your code or schema, I can't provide a better answer.

The SafetyCouncilIds property was the cause of the problem. I changed this to an automatic property and built the string elsewhere and projecting onto the POCO worked like a charm.