This is a scenario I encountered many times, yet didn't find an idiomatic approach for it...
Suppose one would like to use a self-defined self-pred function to filter a seq. This self-pred function returns nil for unwanted elements, and useful information for wanted elements. It is desirable to keep the evaluated self-pred values for these wanted elements.
My general solution is:
;; self-pred is a pred function which returns valuable info
;; in general, they are unique and can be used as key
(let [new-seq (filter self-pred aseq)]
(zipmap (map self-pred new-seq) new-seq))
Basically, it is to call self-pred twice on all wanted elements. I feel it is so ugly...
Wonder if there is any better ways. Much appreciated for any input!
i use this kind of snippet:
(keep #(some->> % self-pred (vector %)) data)
like this:
user> (keep #(some->> % rseq (vector %)) [[1 2] [] [3 4]])
;;=> ([[1 2] (2 1)] [[3 4] (4 3)])
or if you like more verbose result:
user> (keep #(some->> % rseq (hash-map :data % :result)) [[1 2] [] [3 4]])
;;=> ({:result (2 1), :data [1 2]} {:result (4 3), :data [3 4]})