A
List<CodeAndNi> list = new List<CodeAndNi>()
{
new CodeAndNi() {Code = "c1", Ni = ""},
new CodeAndNi() {Code = "c2", Ni = "1"},
new CodeAndNi() {Code = "c3", Ni = "1"},
new CodeAndNi() {Code = "c4", Ni = "2"},
new CodeAndNi() {Code = "c5", Ni = "3"},
new CodeAndNi() {Code = "c6", Ni = "4"},
new CodeAndNi() {Code = "c7", Ni = ""},
new CodeAndNi() {Code = "c8", Ni = "4"}
};
Нужно выбрать только повторяющиеся по полю NI значения, что бы на выходе получился вот такой лист
{Code = "c1", Ni = ""},
{Code = "c7", Ni = ""},
{Code = "c2", Ni = "1"},
{Code = "c3", Ni = "1"},
{Code = "c6", Ni = "4"},
{Code = "c8", Ni = "4"}
Пишу такой запрос