LINQ Grouping to same recipient-CodePudding

i want to Group a List of Mails to their recipients.

The lstMails List is a List<MailModel>

MailModel has a Property which is string[] To.

for example there could be 5 mails in this List.

Mail1.To = ["[email protected]"]
Mail2.To = ["[email protected]", "[email protected]"]
Mail3.To = ["[email protected]"]
Mail4.To = ["[email protected]", "[email protected]"]
Mail5.To = ["[email protected]"]

i would like to get a list for each Mail Recipient.

So for example

"lstNicoTest" = [ Mail1, Mail2 ]
"lstNicoJeff" = [ Mail3, Mail5 ]
"lstNicoFrank" = [ Mail2, Mail4 ]
"lstNicoStar" = [ Mail5 ]

at best it would be a ForEach(List<MailModel> list in lstMails.GroupBy(-----))

i dont know i have been googling around, but the problem is if i Group By it only checks if arrays are the Same, basicly if .To is ["reci1", "reci"] == ["reci1", "reci"] it doesnt not "copy" them basicly

if i did not provide sufficent information im sorry, im here to edit..

CodePudding user response：

You can fetch all recipients, then distinct them and then filter lstMails for the user.

Something like:

lstMails
  .SelectMany(mail => mail.To)
  .Distinct()
  .Select(user => lstMails.Where(mail => mail.To.Contains(user))

CodePudding user response：

I believe this gives the desired result:

var mailsByRecipient = (from m in lstMails
                  from recipient in m.To
                  select new { m, recipient } into s
                  group s by s.recipient into g
                  select new { recipient = g.Key, mails = g.Select(x => x.m) })
                  .ToList();

It returns a list of every unique email recipient, with the list of MailModels it's in.

It achieves that by first creating a cartesian product of each recipient with it's respective MailModel (into s), and uses that to group by recipient (into g).

The last select is purely aesthetical, creating a new object that contains the properties recipient and mails. I find it quirky to work with IGrouping<TKey, TElement> directly.