KeySelect¶ $ wo 'KeySelect[<|1 -> a, 2 -> b, 3 -> c|>, EvenQ]' <|2 -> b|> The operator form KeySelect[crit] applies to an association later. $ wo 'KeySelect[EvenQ][<|1 -> a, 2 -> b, 3 -> c|>]' <|2 -> b|>