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Converting an SQL with Left Join , Group and Sum to a Linq Query

I am trying to replicate the below SQL in C# & Linq , but I am not too experienced with Linq beyond the basics.
SELECT SUM(coalesce(cd.minutesspent,0))
FROM timelabels t
LEFT JOIN challengedetails cd on cd.createddate = t.date
GROUP BY t.date
This would give me a sum of minutes for every date, or zero if there were null entries. Pretty straightforward I think.
// timelabels structure
DateTime start = DateTime.Now.AddDays(-14);
DateTime end = DateTime.Now;
List<DateTime> timelabels = new List<DateTime>();
for (var dt = start; dt <= end; dt = dt.AddDays(1))
{
timelabels.Add(dt);
}
// ChallengeDetails structure & sample data
class ChallengeDetails(){
DateTime? Createddate
int? MinutesSpent
}
List<ChallengeDetails> ChallengeDetails = new List<ChallengeDetails >();
List<ChallengeDetails> ChallengeDetails = new List<ChallengeDetails>();
ChallengeDetails.Add(new ChallengeDetails { MinutesSpent = 44, Createddate = DateTime.Now.AddDays(-10) });
ChallengeDetails.Add(new ChallengeDetails { MinutesSpent = 31, Createddate = DateTime.Now.AddDays(-7) });
ChallengeDetails.Add(new ChallengeDetails { MinutesSpent = 13, Createddate = DateTime.Now.AddDays(-3) });
ChallengeDetails.Add(new ChallengeDetails { MinutesSpent = 77, Createddate = DateTime.Now.AddDays(-2) });
// The Actual Code
List<string> timedata = (from a in timelabels
join al in ChallengeDetails on a equals al.Createddate into All
from al in All.DefaultIfEmpty()
group al by a into grouped
select grouped.Sum(m => m.MinutesSpent ?? 0).ToString()
).ToList();
Looking at this it should work - I have DefaultIfEmpty which should replicate the left join. Within the Sum I have '?? 0' which should be the fallback for any dates that dont have a ChallengeDetail.
But I get System.NullReferenceException: 'Object reference not set to an instance of an object.'
m was null. I shouldnt have gotten this as I have null entries covered or have I got this all wrong ?

Under the section "Actual Code" just add a parenthesis in Sum function, as below
It should take care of null , even before Sum works.
select grouped.Sum(m => (m.MinutesSpent ?? 0)).ToString()

This will do for you, using LINQ - Lambda Expressions:
var TotalMinutesSpentGroupedList = timelabels
.GroupJoin(challengedetails,
t => date,
cd => createddate,
(t,cd) => new
{
MinutesSpent = cd.minutesspent ?? 0,
CreateDate = cd.createddate ?? DateTime.Now
})
.SelectMany(tcd=> challengedetails.DefaultIfEmpty(),
(t, cd) => new
{
MinutesSpent = cd.minutesspent ?? 0,
CreateDate = cd.createddate ?? DateTime.Now
})
.Select(s => new
{
MinutesSpent = cd.minutesspent ?? 0,
CreateDate = cd.createddate ?? DateTime.Now
})
.GroupBy(g => g.createddate).Select(item => item.Sum(s => s.minutesspent));

linq to retrieve name instead of id and list in descending order

can u help me to solve this.
i'm retrieving the balance of each heads, and i retrieved the balance of each heads. Now i want to list the balance in the descending order and list the name instead of h_id. i used the code
protected void account_watchlist() {
using(var context = new sem_dbEntities()) {
//ledger && head
var year = DateTime.Now.AddMinutes(318).Year;
var month = DateTime.Now.AddMinutes(318).Month;
var start = new DateTime();
if (month >= 4) {
start = new DateTime(year, 04, 01);
} else if (month < 4) {
start = new DateTime(year - 1, 04, 01);
}
var qr = (from a in context.ledgers
where a.entry_date >= start && a.entry_date < new DateTime(year, month, 1)
join b in context.heads on a.h_id equals b.h_id
group a by a.h_id into sb select new {
sb.FirstOrDefault().h_id,
totalc = sb.Sum(c => c.credit),
totald = sb.Sum(d => d.debit),
balance = sb.Sum(d => d.debit) - sb.Sum(c => c.credit)
}).ToList();
Repeater2.DataSource = qr.ToList();
Repeater2.DataBind();
}
}

You need to use group join of heads with ledgers. It will give you access both to head entity and all related ledgers (in headLedgers collection):
from h in context.heads
join l in context.ledgers.Where(x => x.entry_date >= startDate && x.entry_date < endDate)
on h.h_id equals l.h_id into headLedgers
where headLedgers.Any()
let totalc = headLedgers.Sum(l => l.credit),
let totald = headLedgers.Sum(l => l.debit),
select new {
h.h_id,
h.name,
totalc,
totald,
balance = totald - totalc,
}
I also introduced two range variables for total credit and total debit (consider better names here) to avoid calculating them second time for balance.

Linq group by month/year with empty months for past 12 months

How would I get this query to get the monthly count data for the past 12 months? I don't want to hard code the range, I want to use the current date DateTime.Now and get all the data for the past 12 months from that. I am trying to avoid adding a calendar table to the database and do this just using LINQ.
Some months might not have any data but I still need a count of 0 for those.
For example. If my data contains
Date Count
12/2/2013, 4
10/1/2014, 1
11/5/2014, 6
The results should be, using the current date of 11/9/2014
11/2013, 0
12/1013, 4
1/2014, 0
2/2014, 0
3/2014, 0
4/2014, 0
5/2014, 0
6/2014, 0
7/2014, 0
8/2014, 0
9/2014, 0
10/2014, 1
11/2014, 6
I can't get it to work. I think it's how I'm using Range but I'm not sure.
TimeSpan ts = new TimeSpan(365, 0, 0, 0);
DateTime yearAgo = DateTime.Now.Subtract(ts);
var changesPerYearAndMonth =
from year in Enumerable.Range(yearAgo.Year, 1)
from month in Enumerable.Range(1, 12)
let key = new { Year = year, Month = month }
join revision in list on key
equals new { revision.LocalTimeStamp.Year,
revision.LocalTimeStamp.Month } into g
select new { GroupCriteria = key, Count = g.Count() };
I have modified the answer from this this link as a starting point.
Linq: group by year and month, and manage empty months
I just found this article that is the same question but unanswered
Linq - group by datetime for previous 12 months - include empty months

To get the past twelve months, use
var now = DateTime.Now;
var months = Enumerable.Range(-12, 12)
.Select(x => new {
year = now.AddMonths(x).Year,
month = now.AddMonths(x).Month });
To be safe you should first move 'now' to the start of the month to avoid any end-of-month effects with AddMonth.
var now = DateTime.Now;
now = now.Date.AddDays(1-now.Day);
Complete example:-
var list = new [] {
new { LocalTimeStamp = DateTime.Parse("12/2/2013"), count = 4},
new { LocalTimeStamp = DateTime.Parse("10/1/2014"), count = 1 },
new { LocalTimeStamp = DateTime.Parse("11/5/2014"), count = 6}
};
var now = DateTime.Now;
now = now.Date.AddDays(1-now.Day);
var months = Enumerable.Range(-12, 13)
.Select(x => new {
year = now.AddMonths(x).Year,
month = now.AddMonths(x).Month });
var changesPerYearAndMonth =
months.GroupJoin(list,
m => new {month = m.month, year = m.year},
revision => new { month = revision.LocalTimeStamp.Month,
year = revision.LocalTimeStamp.Year},
(p, g) => new {month = p.month, year = p.year,
count = g.Sum(a => a.count)});
foreach (var change in changesPerYearAndMonth)
{
Console.WriteLine(change.month + " " + change.year +" " + change.count);
}

You don't need a 3-way join, you just need to filter your data before grouping.
1) Query expression syntax
// since your list item type was not posted, anyway same access as your LocalTimeStamp property
list = new List<DateTime>();
DateTime aYearAgo = DateTime.Now.AddYears(-1);
var dateslastYear = from date in list
where date > aYearAgo
group date by new { date.Year, date.Month } into g
select new { GroupCriteria = g.Key, Count = g.Count() };
2) Chained
dateslastYear = list.Where (d=>d>aYearAgo)
.GroupBy (date=>new{date.Year, date.Month });
3) If you want grouping by year/month pairs, including records of not existent entries, and also omitting those pairs that are older than a year occurring with the joined Enumerable.Range call:
var thisYearPairs = from m in Enumerable.Range(1, DateTime.Now.Month)
select new { Year = DateTime.Now.Year, Month = m };
var lastYearPairs = from m in Enumerable.Range(DateTime.Now.Month, 12 - DateTime.Now.Month + 1)
select new { Year = DateTime.Now.Year - 1, Month = m };
var ymOuter = from ym in thisYearPairs.Union(lastYearPairs)
join l in list on new { ym.Year, ym.Month } equals new { l.Year, l.Month } into oj
from p in oj.DefaultIfEmpty()
select new { a = ym, b = p == null ? DateTime.MinValue : p };
var ymGroup = from ym in ymOuter
group ym by ym into g
select new { GroupCriteria = g.Key.a, Count = g.Key.b == DateTime.MinValue ? 0 : g.Count() };

You are taking the range for the 12 months of last year only but you actually want the last twelve months.
You can do this using a Enumerable.Range and the AddMonths method:
var changesPerYearAndMonth =
from month in Enumerable.Range(0, 12)
let key = new { Year = DateTime.Now.AddMonths(-month).Year, Month = DateTime.Now.AddMonths(-month).Month }
join revision in list on key
equals new
{
revision.LocalTimeStamp.Year,
revision.LocalTimeStamp.Month
} into g
select new { GroupCriteria = key, Count = g.Count() };

public int YearDiff(DateTime a, DateTime b)
{
return (int) Math.Floor((a.Year + a.Month / 100.0 + a.Day / 10000.0) - (b.Year + b.Month / 100.0 + b.Day / 10000.0));
}

c# datatable group by many columns

This is my old code
DateTime epoch = new DateTime(1970, 1, 1);
var result = (from row in InBoundtable.AsEnumerable()
group row by row.Field<string>("Date") into grp
select new
{
AbandonCalls = grp.Sum((r) => Double.Parse(r["AvgAbandonedCalls"].ToString())),
Date = ((DateTime.Parse(grp.Key.ToString())) - epoch).TotalMilliseconds
}).ToList();
as you see, I am making group on Date column.
Can I make the group on Date and Slice columns? where both of them is string value

Create an anonymous type using those two columns. Both columns will be part of the group's "key", so you'll have to access them separately.
DateTime epoch = new DateTime(1970, 1, 1);
var result = (from row in new DataTable().AsEnumerable()
group row by new
{
Date = row.Field<string>("Date"),
Slice = row.Field<string>("Slice")
}
into grp
select new
{
AbandonCalls = grp.Sum((r) => Double.Parse(r["AvgAbandonedCalls"].ToString())),
Date = ((DateTime.Parse(grp.Key.Date)) - epoch).TotalMilliseconds,
grp.Key.Slice
}).ToList();

Group by date range , count and sort within each group LINQ

I have a collection of dates stored in my object. This is sample data. In real time, the dates will come from a service call and I will have no idea what dates and how many will be returned:
var ListHeader = new List<ListHeaderData>
{
new ListHeaderData
{
EntryDate = new DateTime(2013, 8, 26)
},
new ListHeaderData
{
EntryDate = new DateTime(2013, 9, 11)
},
new ListHeaderData
{
EntryDate = new DateTime(2013, 1, 1)
},
new ListHeaderData
{
EntryDate = new DateTime(2013, 9, 15)
},
new ListHeaderData
{
EntryDate = new DateTime(2013, 9, 17)
},
new ListHeaderData
{
EntryDate = new DateTime(2013, 9, 5)
},
};
I now need to group by date range like so:
Today (1) <- contains the date 9/17/2013 and count of 1
within 2 weeks (3) <- contains dates 9/15,9/11,9/5 and count of 3
More than 2 weeks (2) <- contains dates 8/26, 1/1 and count of 2
this is my LINQ statement which doesn't achieve what I need but i think i'm in the ballpark (be kind if I'm not):
var defaultGroups = from l in ListHeader
group l by l.EntryDate into g
orderby g.Min(x => x.EntryDate)
select new { GroupBy = g };
This groups by individual dates, so I have 6 groups with 1 date in each. How do I group by date range , count and sort within each group?

Introduce array, which contains ranges you want to group by. Here is two ranges - today (zero days) and 14 days (two weeks):
var today = DateTime.Today;
var ranges = new List<int?> { 0, 14 };
Now group your items by range it falls into. If there is no appropriate range (all dates more than two weeks) then default null range value will be used:
var defaultGroups =
from h in ListHeader
let daysFromToday = (int)(today - h.EntryDate).TotalDays
group h by ranges.FirstOrDefault(range => daysFromToday <= range) into g
orderby g.Min(x => x.EntryDate)
select g;
UPDATE: Adding custom ranges for grouping:
var ranges = new List<int?>();
ranges.Add(0); // today
ranges.Add(7*2); // two weeks
ranges.Add(DateTime.Today.Day); // within current month
ranges.Add(DateTime.Today.DayOfYear); // within current year
ranges.Sort();

How about doing this?
Introduce a new property for grouping and group by that.
class ListHeaderData
{
public DateTime EntryDate;
public int DateDifferenceFromToday
{
get
{
TimeSpan difference = DateTime.Today - EntryDate.Date;
if (difference.TotalDays == 0)//today
{
return 1;
}
else if (difference.TotalDays <= 14)//less than 2 weeks
{
return 2;
}
else
{
return 3;//something else
}
}
}
}
Edit: as #servy pointed in comments other developers may confuse of int using a enum will be more readable.
So, modified version of your class would look something like this
class ListHeaderData
{
public DateTime EntryDate;
public DateRange DateDifferenceFromToday
{
get
{
//I think for this version no comments needed names are self explanatory
TimeSpan difference = DateTime.Today - EntryDate.Date;
if (difference.TotalDays == 0)
{
return DateRange.Today;
}
else if (difference.TotalDays <= 14)
{
return DateRange.LessThanTwoWeeks;
}
else
{
return DateRange.MoreThanTwoWeeks;
}
}
}
}
enum DateRange
{
None = 0,
Today = 1,
LessThanTwoWeeks = 2,
MoreThanTwoWeeks = 3
}
and use it like this
var defaultGroups = from l in ListHeader
group l by l.DateDifferenceFromToday into g // <--Note group by DateDifferenceFromToday
orderby g.Min(x => x.EntryDate)
select new { GroupBy = g };

Do you specifically want to achieve the solution in this way? Also do you really want to introduce spurious properties into your class to meet these requirements?
These three lines would achieve your requirements and for large collections willbe more performant.
var todays = listHeader.Where(item => item.EntryDate == DateTime.Today);
var twoWeeks = listHeader.Where(item => item.EntryDate < DateTime.Today.AddDays(-1)
&& item.EntryDate >= DateTime.Today.AddDays(-14));
var later = listHeader.Where(item => item.EntryDate < DateTime.Today.AddDays(-14));
also you then get the flexibility of different groupings without impacting your class.
[Edit: in response to ordering query]
Making use of the Enum supplied above you can apply the Union clause and OrderBy clause Linq extension methods as follows:
var ord = todays.Select(item => new {Group = DateRange.Today, item.EntryDate})
.Union(
twoWeeks.Select(item => new {Group = DateRange.LessThanTwoWeeks, item.EntryDate}))
.Union(
later.Select(item => new {Group = DateRange.MoreThanTwoWeeks, item.EntryDate}))
.OrderBy(item => item.Group);
Note that I'm adding the Grouping via a Linq Select and anonymous class to dynamically push a Group property again not effecting the original class. This produces the following output based on the original post:
Group EntryDate
Today 17/09/2013 00:00:00
LessThanTwoWeeks 11/09/2013 00:00:00
LessThanTwoWeeks 15/09/2013 00:00:00
LessThanTwoWeeks 05/09/2013 00:00:00
MoreThanTwoWeeks 26/08/2013 00:00:00
MoreThanTwoWeeks 01/01/2013 00:00:00
and to get grouped date ranges with count:
var ord = todays.Select(item => new {Group = DateRange.Today, Count=todays.Count()})
.Union(
twoWeeks.Select(item => new {Group = DateRange.LessThanTwoWeeks, Count=twoWeeks.Count()}))
.Union(
later.Select(item => new {Group = DateRange.MoreThanTwoWeeks, Count=later.Count()}))
.OrderBy(item => item.Group);
Output is:
Group Count
Today 1
LessThanTwoWeeks 3
MoreThanTwoWeeks 2

I suppose this depends on how heavily you plan on using this. I had/have a lot of reports to generate so I created a model IncrementDateRange with StartTime, EndTime and TimeIncrement as an enum.
The time increment handler has a lot of switch based functions spits out a list of times between the Start and End range based on hour/day/week/month/quarter/year etc.
Then you get your list of IncrementDateRange and in linq something like either:
TotalsList = times.Select(t => new RetailSalesTotalsListItem()
{
IncrementDateRange = t,
Total = storeSales.Where(s => s.DatePlaced >= t.StartTime && s.DatePlaced <= t.EndTime).Sum(s => s.Subtotal),
})
or
TotalsList = storeSales.GroupBy(g => g.IncrementDateRange.StartTime).Select(gg => new RetailSalesTotalsListItem()
{
IncrementDateRange = times.First(t => t.StartTime == gg.Key),
Total = gg.Sum(rs => rs.Subtotal),
}).ToList(),