c# - LINQ: how to aggregate list within object after grouping properties -


i have object chartobject contains list. have list of chartobjects used linq remove duplicate attributes. don't know how combine each"itemlist" property of chartobjects.

public class chartobject {     public string type { get; set; }     public int year { get; set; }     public long cost { get; set; }     public list<items> itemlist { get; set; } }  list<chartobject> colist = getitems();  result = colist.groupby(i => new { i.type, i.year }).select(g => new chartobject {     type = g.key.type,              year = g.key.year,     cost = g.sum(i => i.cost),      itemlist = g.select(i => i.itemlist)    //does not work }).tolist();

i'm assuming it's not simple casting itemlist compiler says , there must sort of aggregation done?

assuming want combine of items in group, you're looking selectmany, , you'll need call tolist list<items>:

g.selectmany(i => i.itemlist).tolist();

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