c# - groupby filtering in linq -

i need groupby query

if (randomize) {     list<tblinvoice> _result = db.tblinvoices.tolist();      var _temp = xxx.where(p => (p.ispostalpayment == null || p.ispostalpayment == false)).tolist();     _result = _temp.orderby(o => guid.newguid()).take(5).tolist();     _result = _result.groupby(x => x.cuserid).tolist();     return _result; } 

when use groupby in query, error when use groupby in query, under error

cannot implicitly convert type 'system.collections.generic.list>' 'system.collections.generic.list'

the type of _result list<tblinvoice>. here

_result = _temp.orderby(o => guid.newguid()).take(5).tolist(); 

you have no problem. order invoices , take 5 of them create new list<tblinvoice>.

however, here

_result = _result.groupby(x => x.cuserid).tolist(); 

there problem. groupby return sequence of igrouping<tkey,telement> objects , calling tolist create list of type of objects , not list<tblinvoice>. can't assign reference of list of type variable can hold references list<tblinvoice> objects.