generics - C# List<object>.RemoveAll() - How to remove a subset of the list? -

i have 2 classes feeds_auto , product multiple matching properties. particular problem, autoid field need use.

i have list<feedsauto> several hundred unique entries. have small list<product> 10, 20 unique entries. want remove items in small list large list.

how use removeall({lambda expression}) accomplish this? of examples have found depend on generic list being of simple types (strings, ints, etc).

private static int doinserts(ref list<model.feeds_auto> source, ref list<model.product> target, guid companyid) {     list<model.product> newproductlist = new list<model.product>();     list<model.product> dropsourcelist = new list<model.product>();      using (var db = helpers.getproddb())     {         foreach (var src in source)         {             var tgt = target.where(a => a.alternateproductid == src.autoid && a.lastfeedupdate < src.datemodified).firstordefault();             if (tgt == null)             {                 newproductlist.add(new model.product{...});                 dropsourcelist.add(src);             }         }         db.savechanges();          if (dropsourcelist.count > 0)         {             source.removeall(????);         }     } } 

to in loop not difficult:

foreach (var drop in dropsourcelist) {     source.removeall(a => a.autoid == drop.autoid); } 

it not make sense (to me) loop on set call removeall 1 item in each pass.

you can use any simplify

source.removeall(a => dropsourcelist.any(b => a.autoid == b.autoid)); 

you can reduce looping creating hashset of id's first:

var toremove = new hashset<int>(dropsourcelist.convertall(a => a.autoid));  source.removeall(a => toremove.contains(a.autoid));