if I understood correctly you're looking for 'fnil' :
=>(update-in {} [:foo :bar] (fnil conj []) :a :b :c)
{:foo {:bar [:a :b :c]}}
Jim
On 05/04/13 12:25, Simon Katz wrote:
Hi.Is there an idiomatic way to have update-in create a vector when the supplied keys do not already exist? (Or maybe I should use something other than update-in?)For example... This gives me a sequence of things in the reverse of the order I want: (update-in {} [:foo :bar] conj :a) ;; => {:foo {:bar (:a)}} (update-in *1 [:foo :bar] conj :b) ;; => {:foo {:bar (:b :a)}}This does what I want, but at the expense of creating a new vector each time:(update-in {} [:foo :bar] (comp vec conj) :a) ;; => {:foo {:bar [:a]}} (update-in *1 [:foo :bar] (comp vec conj) :b) ;; => {:foo {:bar [:a :b]}}(I know about laziness and structure sharing, and that this expense may not be large.)The following works, but at the expense of a new function that the reader has to understand:(defn conj-vec "Like conj, but returns a vector if coll is empty. Useful in conjunction with update-in." [coll x] (if (empty? coll) [x] (conj coll x))) (update-in {} [:foo :bar] conj-vec :a) ;; => {:foo {:bar [:a]}} (update-in *1 [:foo :bar] conj-vec :b) ;; => {:foo {:bar [:a :b]}} Is there a better way? -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to [email protected]Note that posts from new members are moderated - please be patient with your first post.To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/clojure?hl=en ---You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].For more options, visit https://groups.google.com/groups/opt_out.
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