The correct pattern for Cases

I have a problem that, admittedly, I have already solved using Select instead, but it is irking me that I cannot seem to construct the right pattern to solve it using Cases. I would like the output of

Cases[
    {{{1, 2}, {3}, {4, 5}}, {{6}, {}}, {{}, {}}},
    (* THE CORRECT PATTERN HERE *)
]

to be

{{{1, 2}, {3}, {4, 5}}, {{6}, {}}}

In other words, I would like a pattern that picks up all the elements of the outer list that have at least one non-empty list as an element.

Thanks in advance for your help.

Answer

list = {{{1, 2}, {3}, {4, 5}}, {{6}, {}}, {{}, {}}};
Cases[list, Except[{{} ..}]]
(* {{{1, 2}, {3}, {4, 5}}, {{6}, {}}} *)

Cases[list, {___, Except[{}], ___}]
(* {{{1, 2}, {3}, {4, 5}}, {{6}, {}}} *)

You can also use PatternTest (_?func) where func is any selector function that you might have used as the second argument of Select. For example:

Select[list, Union @@ # =!= {} &]  (* or Flatten @ # =!= {} & or  ... *)
(* {{{1, 2}, {3}, {4, 5}}, {{6}, {}}}  *)

Cases[list, _?(Union @@ # =!= {} &)]
(*  {{{1, 2}, {3}, {4, 5}}, {{6}, {}}} *)

Comments

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