GatherBy¶ Groups elements by applying a function, maintaining order of first appearance. $ wo 'GatherBy[{1, 2, 3, 4, 5}, EvenQ]' {{1, 3, 5}, {2, 4}} $ wo 'GatherBy[{-2, -1, 0, 1, 2}, Sign]' {{-2, -1}, {0}, {1, 2}}