(def keep-identity-2 (partial keep (comp seq (partial keep identity))))

keep-identity-2 is like (keep identity ...) but squared. We have a sequence of sequences and we want to keep only non-nil elements in those sequences. If the whole nested sequence becomes empty, we want to exclude it from the result.

(keep-identity-2 (repeat 3 (range 5)))
=> ((0 1 2 3 4) (0 1 2 3 4) (0 1 2 3 4))

(keep-identity-2 [[1 false 2 nil 3] [nil nil] [4 5]])
=> ((1 false 2 3) (4 5))