LINQ DataTable Sum In Where Clause

Question

I'm having a rough time figuring out exactly how to do a LINQ query on a DataTable and return a full row while having the WHERE clause test on a sum.

My code:

transactionsToRemove.AddRange(paymentTransactionResults
     .AsEnumerable()
     .Where(...)
     .GroupBy(r => (decimal)r["AccountNumber"]));

There are multiple transactions for each AccountNumber, and I need to sum those together and determine whether they're less than a user inputted amount (For my purpose, it's called balanceGreaterThan). I can't find any examples to go by where someone has done this sort of thing.

Thanks in advance, SO.

Edit: My apologies -- The column I need to sum is called "Balance"

Edit 2: Final code

transactionsToRemove.AddRange(paymentTransactionResults
     .AsEnumerable()
     .GroupBy(r => r.Field<string>("AccountNumber"))
     .Where(g => g.Sum(r => r.Field<decimal>("Balance")) < balanceGreaterThan)
     .SelectMany(g => g));

I had to change the GroupBy to use r.Field rather than r["AccountNumber"]

Answer 1

transactionsToRemove.AddRange(paymentTransactionResults
     .AsEnumerable()
     .GroupBy(r => (decimal)r["AccountNumber"])
     .Where(g => g.Sum(r => (decimal)r["Balance"]) <= someInput)
     .SelectMany(g => g));

Answer 2

You're trying to filter the groups themselves (to find which groups have a large sum), not the rows that go into the groups.
Therefore, you need to put the Where() call after the GroupBy:

transactionsToRemove.AddRange(paymentTransactionResults
     .AsEnumerable()
     .GroupBy(r => (decimal)r["AccountNumber"])
     .Where(g => g.Sum(r => r.Field<decimal>("Balance") < balanceGreaterThan));

EDIT: If you want to get an IEnumerable<DataRow> back (as opposed to an IEnumerable<IGrouping<DataRow>>), you'll need to add .SelectMany(g => g).

Answer 3

I think you want something like:

transactionsToRemove.AddRange(paymentTransactionResults 
     .AsEnumerable() 
     .GroupBy(r => (decimal)r["AccountNumber"])); 
     .Where(grp => grp.Sum(r => r["amount"]) < balanceGreaterThan);