LINQ groupby when two attributes are the same

Question

So i have two objects that i join together but on some occasions lines from object x will have two properties that will be the duplicates on another object so for simplicity we can call them PropertyOne and PropertyTwo and when those two are the same i want to group them together into one line and take the sum of the amount field the two objects have

i have this linq where without the groupby part it works to get all lines but it then have the objects where the properties are the same as their own "lines" and not the same. How would i change this to make it group them properly

 transactions = (from x in data.Transactions join y in data.OtherTransactions on x.TransId equals y.TransId group x by x.PropertyOne, x.PropertyTwo select new OtherFinancialTransactionsItems { Description = x.Description, LineAmount = y.Amount }).ToList();

Sample data

data.Transactions = [ {Transaction: TransId: 1, Description: "Foo", PropertyOne: "123", PropertyTwo: "100"}, {Transaction: TransId: 2, Description: "Blah", PropertyOne: "456", PropertyTwo: "200"}, {Transaction: TransId: 3, Description: "Foo", PropertyOne: "123", PropertyTwo: "100"} ] data.OtherTransactions = [ {OtherTransactions: TransId: 1, Amount: 5000}, {OtherTransactions: TransId: 2, Amount: 7500}, {OtherTransactions: TransId: 3, Amount: 5000} ]

And the expected outcome would be two lines

OtherFinancialTransactionsItems [ {OtherFinancialTransactionsItem: Description: "Foo", Amount: 10000}, {OtherFinancialTransactionsItem: Description: "Blah", Amount: 7500}, ]

Based on your expected outcome, it seems like you want to be grouping on x.Description, not x.PropertyOne, x.PropertyTwo. Otherwise it doesn't make sense as your group (by x.PropertyOne, x.PropertyTwo) could be comprised of elements with different Description values. — Flater
– Flater, Commented Apr 1, 2021 at 14:47
@Flater mm8 answer is correct for this with the only piece i needed to add where description also in grouping because it ended up being that i needed all three of those properties to be the same — novafluff
– novafluff, Commented Apr 1, 2021 at 14:49

mm8 · Accepted Answer · 2021-04-01 14:38:49Z

This should work if I understand your requirements correctly:

transactions = (from x in data.Transactions join y in data.OtherTransactions on x.TransId equals y.TransId let temp = new { x.Description, y.Amount, x.PropertyOne, x.PropertyTwo } group temp by new { x.PropertyOne, x.PropertyTwo } into g select new OtherFinancialTransactionsItems { Description = g.First().Description, LineAmount = g.Sum(x => x.Amount) }).ToList();

Svyatoslav Danyliv · Accepted Answer · 2021-04-01 13:29:12Z

You have to group only records which have these properties equal. And concatenate with records with not equal.

var joined = from x in data.Transactions join y in data.OtherTransactions on x.TransId equals y.TransId select new { x, y }; var withEqual = from q in joined where q.x.PropertyOne == q.x.PropertyTwo group q by new { q.x.PropertyOne, x.Description } into g select new { g.Key.Description, LineAmount = g.Sum(m => m.y.Amount) } var notEqual = from q in joined where q.x.PropertyOne != q.x.PropertyTwo select new { q.x.Description, LineAmount = q.y.Amount } var transactions = withEqual .Concat(notEqual) .Select(x => new OtherFinancialTransactionsItems { Description = x.Description, LineAmount = y.Amount }) .ToList();

This query is close to your requirement, but I think you have missed something.

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