I have a for each loop to get data which is very time consuming.any suggestion to convert this to linq. Thanks in advance.
iListReport = obj.GetClosedReports();
string sRepType ="";
foreach (ReportStatisticsInfo item in reportStatistic)
{
sRepType = item.ReportName.Trim();
IList<string> lastClosedReport = new List<string>();
foreach (TaskListInfo taskInfo in iListReport)
{
string reportName = taskInfo.DocumentName.Trim();
if (string.Compare(sRepType, reportName, true) == 0)
{
if (taskInfo.ActionID == Convert.ToInt16(ReportAction.Close) && !lastClosedReport.Contains(taskInfo.DocumentID))
{
iClosedreportCount += 1;
lastClosedReport.Add(taskInfo.DocumentID);
}
}
}
}
Here you go. I've done a pretty literal translation of your code into LINQ which will hopefully help you to see how I've converted it.
Note the use of the let keyword which allows you to declare a range variable (which allows you to perform your trim once and then use the result in multiple places).
Also note the use of group by at the bottom of the LINQ query to ensure we only take the first occurence of each documentID.
IList iListReport = obj.GetClosedReports();
var query = from item in reportStatistic
let sRepType = item.ReportName.Trim()
from taskInfo in iListReport
let reportName = taskInfo.DocumentName.Trim()
where string.Compare(sRepType, reportName, true) == 0
&& taskInfo.ActionID == Convert.ToInt16(ReportAction.Close)
//here's how we make sure we don't get the same documentID twice
//we group by the id and then take the first
group taskInfo by taskInfo.DocumentID into grouping
select grouping.First().DocumentID;
var lastClosedReport = query.ToList();
iClosedreportCount = lastClosedReport.Count;
How to convert a foreach loop to LINQ
Here are some comparisons of your code against LINQ version to help you out if you've got to do a conversion again sometime. Hopefully this will help anyone else out there that has got to convert a foreach loop to LINQ.
1. foreach and from
You can perform a straight swap of the foreach clause for a LINQ from clause. You can see that this:
foreach (ReportStatisticsInfo item in reportStatistic)
has become this:
from item in reportStatistic
2) Variable declaration and the let keyword
When you declare variables within your foreach, you can swap them out for the LINQ let statement. You can see that this declaration:
sRepType = item.ReportName.Trim();
has become:
let sRepType = item.ReportName.Trim()
3) if statements and the where clause
Your if statements can go inside the where clause. You can see that the following two if statements:
if (string.Compare(sRepType, reportName, true) == 0)
if (taskInfo.ActionID == Convert.ToInt16(ReportAction.Close)
have become this where clause
where string.Compare(sRepType, reportName, true) == 0
&& taskInfo.ActionID == Convert.ToInt16(ReportAction.Close)
4) Using group by to remove duplicates.
It's all been quite simple so far because everything has just been a straight swap. The most tricky part is the bit of code where you prevent duplicates from appearing in your result list.
if (taskInfo.ActionID == Convert.ToInt16(ReportAction.Close)
&& !lastClosedReport.Contains(taskInfo.DocumentID))
{
iClosedreportCount += 1;
lastClosedReport.Add(taskInfo.DocumentID);
}
This is tricky because it's the only part that we have to do a bit differently in LINQ.
Firstly we group the 'taskInfo' by the 'DocumentID'.
group taskInfo by taskInfo.DocumentID into grouping
Then we take the first taskInfo from each grouping and get it's ID.
select grouping.First().DocumentID;
A note about Distinct
A lot of people try to use Distinct to get rid of duplicates. This is fine when we're using primitive types, but this can fail when you're using a collection of objects. When you're working with objects Distinct will do a reference comparison of the two objects. This will fail to match objects that are different instances but happen to have the same ID.
If you need to remove duplicates based upon a specific property within an object, then the best approach is to use a group by.
With LINQ you'll get a single IEnumerable<string> with duplicates
from item in reportStatistic
from taskInfo in iiListReport
where (string.Compare(item.ReportName.Trim(), taskInfo.DocumentName.Trim(), true) == 0)
&& taskInfo.ActionID == Convert.ToInt16(ReportAction.Close)
select taskInfo.DocumentID
You can then Distinct().GroupBy(d => d.taskInfo)
Related
How do you index an IQueryable?
I am using a LINQ to sql query to get in values from a particular column. The query is as follows,
var intitalQuery = (from a in sql.GetTable<Staff_Time_TBL>()
where a.Info_Data == SelectedOption
select a.Staff_No).Distinct();
From there I want to be able index the intitalQuery variable and get values as needed.
That value is then used in another query.
My first try was this,
Column1.DataContext = sql.Staff_Time_TBLs.Where(item =>
item.Section_Data == SelectedOption &&
item.Staff_No == intitalQuery[0];
Then I tried this from here with no luck.
Column1.DataContext = sql.Staff_Time_TBLs.Where(item =>
item.Section_Data == SelectedOption &&
item.Staff_No == intitalQuery.First());
From what I can from the link is that that way gets just the first value, I want to be able to get all values via indexing. How do you go about that?
IQueryable<T> inherits from IEnumerable and as such has a wealth of extension methods to accomplish almost anything you'd need from a sequence. In particular, .ToList() turns an enumerable into a List<T> that allows efficient indexing.
.ToList() is slightly more efficient than the more obvious .ToArray() when working with sequences of unknown initial length, because .ToArray() requires an additional copy to end up with an array of exactly the right size. (But arrays are faster to loop over, so it all depends on what you're doing.)
You can do this:
public static List<Staff_Time_TBLs> GetIndexed(string staffNo){
var stuff = sql.Staff_Time_TBLs.Where(item =>
item.Section_Data == SelectedOption &&
item.Staff_No == staffNo;
return stuff.ToList();
}
//to use it...
initialQuery.ForEach(p=>{
var indexvalue = GetIndexed(p)
});
The following code shows how I am assigning data into IEnumerable<UnCompletedJobDetailsBO>.
There is a list (IEnumerable<UnCompletedJobDetailsBO>) that has another list (List<JobDetailsBO>), with that child list (List<JobDetailsBO>) having a list on it. But the AllocationDetailList only ever has one list item.
public IEnumerable<UnCompletedJobDetailsBO> GetControlDetails(DateTime startDate)
{
var controlDetails =
(from booking in db.BookingDetail
where booking.BookingDateTime >= startDate
orderby booking.DocketNo
select new UnCompletedJobDetailsBO()
{
CustomerName = booking.Customer.Name,
CompanyName = booking.CompanyDetail.Name,
JobList =
(from job in db.BookingJob.Where(x => x.BookingID == booking.BookingID) //get job list
select new JobDetailsBO()
{
JobID = job.JobID,
JobType = job.JobType,
ItemName = job.ItemName,
AllocationDetailList =
(from jobAllocationDetail in db.JobAllocation
join returnUnCollected in db.JobReturnUnCollected
on jobAllocationDetail.JobAllocationDetailID
equals returnUnCollected.JobAllocationDetailID
into returnJob
from returnUnCollected in returnJob.DefaultIfEmpty()
where (jobAllocationDetail.Booking.BookingID == booking.BookingID)
select new AllocationBO()
{
JobUnCollectedID = returnJob.JobUnCollectedID,
JobType = jobAllocationDetail.JobType,
CurrentStatus = jobAllocationDetail.CurrentStatus,
}).DefaultIfEmpty().ToList(),
}).DefaultIfEmpty().ToList(),
}).ToList();
return controlDetails;
}
I want to remove the JobList item if the inner list (AllocationDetailList) item satisfies the condition below. Sometimes AllocationDetailList may be null, so I check that also. But when I write below query, it does not remove that particular JobList item that satisfies the condition. Thanks in advance.
public List<UnCompletedJobDetailsBO> RemovePODFromSelectedList(
List<UnCompletedJobDetailsBO> unCompletedJobDetailsBO)
{
unCompletedJobDetailsBO
.SelectMany(y => y.JobList)
.ToList()
.RemoveAll(x => ((x.AllocationDetailList[0] != null) ?
x.AllocationDetailList[0].JobType == "D" &&
x.AllocationDetailList[0].JobUnCollectedID == null &&
x.AllocationDetailList[0].CurrentStatus == 5 :
x.AllocationDetailList.Count > 1));
return unCompletedJobDetailsBO;
}
Without a good, minimal, complete code example, I'm not sure that any performance concern can be addressed. It's hard enough to fully understand the question as it is, but without being able to actually test the code, to reproduce and observe a specific performance concern, it's hard to know for sure where your concern specifically lies, never mind how to fix it.
That said, from the code you posted, it is clear why items are not being removed from the list. The basic issue is that while the SelectMany() method does have the effect of allowing you to enumerate all of the elements from all of the different JobList objects as a single enumeration, the elements are enumerated as a new enumeration.
When you call ToList(), you are creating a whole new list from that new enumeration, and when you call RemoveAll(), you are only removing elements from that new list, not the lists from which they originally came.
You say you can get it to work with a for loop. I assume you mean something like this:
public List<UnCompletedJobDetailsBO> RemovePODFromSelectedList(
List<UnCompletedJobDetailsBO> unCompletedJobDetailsBO)
{
foreach (var item in unCompletedJobDetailsBO)
{
item.JobList.RemoveAll(x => ((x.AllocationDetailList[0] != null) ?
x.AllocationDetailList[0].JobType == "D" &&
x.AllocationDetailList[0].JobUnCollectedID == null &&
x.AllocationDetailList[0].CurrentStatus == 5 :
x.AllocationDetailList.Count > 1));
}
return unCompletedJobDetailsBO;
}
Note: there is no need to return unCompletedJobDetailsBO. That entire object is unchanged, never mind the variable. The only thing the code is modifying is each individual JobList object within the passed-in object's members. I.e. the above method could actually have a return type of void, and the return statement could be removed entirely.
It is possible you could speed the code up by removing the elements in a different way. The List<T>.RemoveAll() method is in fact reasonably efficient, with O(n) cost. But it still involves copying all of the data in the list after the first element that is removed (so that all the elements are shifted down in the list). If you have to have the list ordered, this may be as good as you can do, but if not, you could process the removal differently, or use a different data structure altogether, something unordered where removal of one or more elements costs less.
But again, without more details and without a good example to work with addressing that particular issue doesn't seem practical here.
The condition
x.AllocationDetailList[0] != null
will throw exception if there is no item in the AllocationDetailList. Instead you need to check
x.AllocationDetailList!=null && x.AllocationDetailList.Count>0.
Also .ToList() after SelectMany in your code will create a new list and items will be removed from that new list instead of unCompletedJobDetailsBO. You need to modify the remove function as below
unCompletedJobDetailsBO.ForEach(y => y.JobList.RemoveAll(x => ((x.AllocationDetailList != null && x.AllocationDetailList.Count>0)
?
x.AllocationDetailList[0].JobType == "D"
&& x.AllocationDetailList[0].JobUnCollectedID == null
&& x.AllocationDetailList[0].CurrentStatus == "5"
:
x.AllocationDetailList.Count > 1
)
));
I'm attempting to merge two lists of different objects where a specific field (employeeID) is equal to a specific field[0,0] in another list. My code looks like this:
int i = Users.Count() - 1;
int i2 = oracleQuery.Count() - 1;
for (int c = 0; c <= i; c++)
{
for (int d = 0; d <= i2; d++)
{
if (Users[c].getEmployeeID().ToString() == oracleQuery[d][0,0].ToString())
{
Users[c].setIDMStatus(oracleQuery[d][0,1].ToString());
}
}
}
This works... but it doesn't seem efficient. Any suggestions for more efficient code that will ultimately lead to the Users list containing the new information from the oracleQuery list?
You could use a join with Enumerable.Join:
var matches = Users.Join(oracleQuery,
u => u.getEmployeeId().ToString(),
oq => oq[0,0].ToString(),
(u,oc) => new { User = u, Status = oc[0,1].ToString() });
foreach(var match in matches)
match.User.setIDMStatus(match.Status);
Note that you could eliminate the ToString() calls if getEmployeeId() and the oracleQuery's [0,0] element are of the same type.
The only thing I notice as far as efficiency is that you use the Enumerable.Count() method, which enumerates the results before you loop through again explicitly in your for loops. I think the LINQ implementation will get rid of the pass through the results to count the elements.
I don't know how you feel about using LINQ QUERY EXPRESSIONS, but this is what I like best:
var matched = from user in Users
join item in oracleQuery on user.getEmployeeID().ToString() equals item[0,0].ToString()
select new {user = user, IDMStatus = item[0,1] };
foreach (var pair in matched)
{
pair.user.setIDMStatus(pair.IDMStatus);
}
You could also use nested foreach loops (if there are multiple matches and set is called multiple times):
foreach (var user in Users)
{
foreach (var match in oracleQuery.Where(item => user.getEmployeeID().ToString() == item[0,0].ToString()) {
user.setIDMStatus(match[0,1]);
}
}
Or if there will only be one match for sure:
foreach (var user in Users)
{
var match = oracleQuery.SingleOrDefault(item => user.getEmployeeID().ToString() == item[0,0].ToString());
if (match != null) {
user.setIDMStatus(match[0,1]);
}
}
I don't think there is any real efficiency problem in what you've written, but you can benchmark it against the implementation in LINQ. I think that using foreach or a Linq query expression might make the code easier to read, but I think there is not a problem with efficiency. You can also write the LINQ query expression using LINQ method syntax, as was done in another answer.
If the data comes from a databases you could do a join there. Otherwise, you could sort the two lists and do a merge join that would be faster than what you have now.
However, since C# introduced LINQ there are a lot of ways to do this in code. Just look up using linq to join/merge lists.
I have two main tables Listings and Place . In listing table there is a field PlaceId which referes to a Place entity/row/object . I want to query on both tables so that i get both of them like this .
var query = context.Listings
.Include("Place")
.Where(l => l.Place.TypeId == Type.Ro)
.OrderBy(l => l.Id).ToList();
after this now i want to put some filter on this query , here is the condition .
i got only a string like this var filter = "1,2,4"; . Now i want to filter on listing to gett all these listing where bedroom is equal to 1 OR 2 OR 4 .
What i have done
string minBeds = "1,2,4";
foreach (var item in minBeds.Split(','))
{
int minBed = int.Parse(item);
query = query.Where(l=>l.Place.Bedroom == minBed).ToList();
}
But doing this is giving me Zero result.
The problem with the way you're filtering it. After the first pass, you're filtering out everything except where Bedroom == 1, on the second pass you're filtering out everything except where Bedroom == 2, but since the only items in the list have Bedroom == 1, you won't have anything in the result set.
The solution is to use the conventional C# || operator:
query = query.Where(l => l.Place.Bedroom == "1" ||
l.Place.Bedroom == "2" ||
l.Place.Bedroom == "4");
Or if you want to be more flexible, use the Contains method:
string[] minBeds = "1,2,4".Split(',');
query = query.Where(l => minBeds.Contains(l.Place.Bedroom));
Note if Bedroom is an integer, you'll need to convert the input to an appropriate type first:
var minBeds = "1,2,4".Split(',').Select(int.Parse);
query = query.Where(l => minBeds.Contains(l.Place.Bedroom));
Also note, I've eliminated the ToList here. Unless you need to access items by index and add / remove items from the result collection, it's most likely just a waste of resources. You can usually rely on Linq's native laziness to delay processing to query until you really need the result.
I have a multiselection box and I would like to iterate over the selected items and do a linq query, but I'm not sure how to write it. This is what I have so far:
if (lbStateLegislation.Items.Count > 0)
{
foreach (ListItem li in lbStateLegislation.Items)
attributes = vdc.attributes.Where(a => a.fieldvalue == li.Value).ToList();
}
I basically need to construct an OR query, so it is selecting from the collection where there are values for each of the selected items. I think, as it's written now, it is doing an AND query.
Just use the Contains extension method. Linq2Sql will translate it as an IN clause:
var inValues = lbStateLegislation.Items.Select(s => s.Value);
vdc.attributes.Where(a => inValues.Contains(a.fieldvalue));
You may be able to combine the two statements into one, but I will leave that for you to try as I'm not positive that it will work as a single statement.
HTH
var attributes=
vdc.attributes.Where(q=>
lbStateLegislation.Items.Any(o=> o.Value == q.fieldValue))
.Select(o=> o);