On Sunday 14 December 2008 11:08, Randall R Schulz wrote: > Hi, > > I ran into a special case that I'd like to avoid. When (filter ...) > is either applied to an empty collection or the filter predicate > returns false for all the elements in the supplied collection, filter > returns nil. > > Would it be acceptable and desirable for it to return and empty list > in this case?
To make the case concrete and possibly get a suggestion of a better way to deal with the situation I encountered, here the function that ran into the "nil return from (filter ...)" condition. It uses (flatten ...) from clojure.contrib.seq-utils: This was my original function. It return [nil] when no matching slots are found: (defn- gather-slot-values "Extract all the values paired with the specified key; returns a vector of flattened values" [slot-key c-pairs] (into [] (flatten (map #(second %) (filter #(= (first %) slot-key) c-pairs)))) ) Here's how I modified it so it returns [] in that case: (defn- gather-slot-values "Extract all the values paired with the specified key; returns a vector of flattened values" [slot-key c-pairs] (let [filtered (filter #(= (first %) slot-key) c-pairs)] (if filtered (into [] (flatten (map #(second %) filtered))) [])) ) --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
