Generic List items Subtraction problem

Question

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Sorry
now
Updated ----
hi all please give me the solution for this problem

i have two generic list having Data from two classes using GetAll Functions

i extracted two fields by using LINQ from both Class type Generic List.
LINQ Resultset have two fields in both Lists from them i need to data .

same columns .
monthId ,
Amount

first list have main records for a student month wise fee
while second have concessional record for that student month wise Concessional fee

like

List1 contains

MonthId | Amount
1 | 1000
4 | 500
7 | 1000
10 | 500

And List 2 Contains records like

MonthId | Amount
1 | 100
4 | 50

So i need to get Subtracted results like

MonthId | Amount
1 | 900
4 | 450
7 | 1000
10 | 500

Please give solution how i perform this ..

What should i do to get Result Set .

LINQ can help i tried but did not get right result in another var list
please give me a sloution

thnx

Posted 25-Apr-12 3:31am

gauravupadhyay

Updated 25-Apr-12 5:15am

v4

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Comments

Sergey Alexandrovich Kryukov 25-Apr-12 10:43am

What is the exact type of your "generic list"? I never heard that a list could have columns... :-)
--SA

gauravupadhyay 25-Apr-12 11:49am

@ SAKryukov --
did you understand question ??

4 solutions

Solution 2

Greetings;

In addition to VJ Reddy's solution, I think an extension method along the following lines might be an option for you as well. The extension method is called using a LINQ query for each of the object references that has an update pending inside a foreach() loop:

(Note: The following code fragments were written in LINQPad -www.linqpad.net)

C#

class MonthlyAmount
{
    public int MonthID {get; set;}
    public decimal Amount {get; set;}

    public MonthlyAmount(int Month, decimal Amount)
    {
        this.MonthID = Month;
        this.Amount = Amount;
    }
};

static class Extension
{
    public static void Update<t>(this T Item, Action<t> UpdateAction)
    {
        UpdateAction(Item);
    }
};

void Main()
{
    List<monthlyamount> monthlyAmountsList = new List<monthlyamount>();

    if (monthlyAmountsList == null)
    {
        return;
    }

    monthlyAmountsList.Add(new MonthlyAmount (1, 1000));
    monthlyAmountsList.Add(new MonthlyAmount (4, 500));
    monthlyAmountsList.Add(new MonthlyAmount (7, 1000));
    monthlyAmountsList.Add(new MonthlyAmount (10, 500));

    monthlyAmountsList.Dump();

    List<monthlyamount> monthlyUpdatesList = new List<monthlyamount>();

    if (monthlyUpdatesList == null)
    {
        return;
    }

    monthlyUpdatesList.Add(new MonthlyAmount (1, 100));
    monthlyUpdatesList.Add(new MonthlyAmount (4, 50));

    monthlyUpdatesList.Dump();

    foreach(MonthlyAmount monthlyUpdate in monthlyUpdatesList)
    {
        (from entry in monthlyAmountsList
         where entry.MonthID == monthlyUpdate.MonthID
         select entry).First().Update(updatedEntry => updatedEntry.Amount -= monthlyUpdate.Amount);
    }

    monthlyAmountsList.Dump();

    return;
}

And the Lists<> before the Update Extension is executed contain:

monthlyAmountsList List<MonthlyAmount> (4 items)

MonthID Amount
1 1000
4 500
7 1000
10 500

monthlyUpdatesList List<MonthlyAmount> (2 items)

MonthID Amount
1 100
4 50

The contents of the Updated List<> after the foreach() loop would be as follows:

monthlyAmountsList List<MonthlyAmount> (4 items)

MonthID Amount
1 900
4 450
7 1000
10 500

I hope this was of help and interest to you.

Best Regards...

Posted 25-Apr-12 6:28am

ClockEndGooner

Updated 25-Apr-12 6:32am

v3

Solution 4

C#

list1.forech(item => {
for (int i=0; i<=list2.count;i++)
if(item.monthid == list2[i].monthid)
item.amont -= list2[i].monthid;
};)

Posted 30-Apr-12 23:06pm

mhsefati

Updated 1-May-12 16:44pm

v2

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VJ Reddy · Accepted Answer · 2012-04-25T05:59:00

The following code can be used to obtain the result set specified in the question

C#

void Main()
{
    List<fee> list1 = new List<fee> {
    	new Fee(1,1000),new Fee(4,500),
    	new Fee(7,1000),new Fee(10,500)
    };
    List<fee> list2 = new List<fee> {
    	new Fee(1,100),new Fee(4,50)
    };
    var resultSet = list1.Select (fee => 
    	new Fee(fee.MonthId, fee.Amount - 
    	list2.FirstOrDefault (f => f.MonthId==fee.MonthId).Amount)
    ).ToList();
}
public struct Fee{
    public int MonthId;
    public decimal Amount;
    
    public Fee(int monthId, decimal amount){
    	MonthId = monthId;
    	Amount = amount;
    }
}
//resultSet is List<fee>
//MonthId Amount
// 1 	  900 
// 4 	  450 
// 7	 1000 
//10	  500

Note:
The FirstOrDefault extension method of IEnumerable interface returns the First found value satisfying the predicate or the default value of the item. In this case the Fee struct is Value type, hence we get Amount = 0 for the default item, when the MonthId is not present in list2.

If the Fee is a class, then when the MonthId is not present in list2, null will be returned, as the default value for reference type is null. In such case we have check for null, before deducting the amount from list2 from the amount of list1.

gauravupadhyay · Accepted Answer · 2012-04-25T22:02:00

dear VJ Sir

You are right i am getting null reference problem .

my code is :

for first List

C#

var lisFeeStrdetail = listditinct.GroupBy(x => new { x.MonthId }).Select(group => new { monthId = group.Key.MonthId, Feesum = group.Sum(x => x.Amt) });

and for Second List



    var concessionAmount = from c in lFeeConcessionDetails2
                           orderby c.MonthId ascending
                           select new { MonthId = c.MonthId, Feesum = c.Amount };



and for result Set



if (concessionAmount.Count() != 0) 

   {
                               
 var resultSet = lisFeeStrdetail.Select(a => new { monthId = a.monthId, Feesum = a.Feesum -  concessionAmount.FirstOrDefault(f => f.MonthId == a.monthId).Feesum  } ).ToList();

  }

getting object reference not set to an instance of an Object exception

what are possible mistakes i am doing Please help .

thnx

Generic List items Subtraction problem

4 solutions

Solution 1

Solution 2

Solution 4

Solution 3

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