What you are attempting to do is sometimes called "bashing a transient in
place". See these links for some discussion and examples:
http://clojuredocs.org/clojure_core/clojure.core/assoc!
http://clojuredocs.org/clojure_core/clojure.core/dissoc!
Andy
On Sat, May 11, 2013 at 3:51 PM, Wojciech Winogrodzki <
wwinogrod...@gmail.com> wrote:
> Clojure 1.5.1.
>
> I'm trying to reorder a map. The keys in the map are known beforehand and
> their order is undefined. So, I'm taking this map and construct a new
> transient map with the keys ordered as I need them:
>
> defn reorder-map []
> (let [
> m {:j 10 :g 7 :b 2 :d 4 :e 5 :h 8 :i 9 :f 6 :c 3 :a 1 }
> kwds [:a :b :c :d :e :f :g :h :i :j]
> temp (transient {})
> ]
> (doseq [k kwds]
> (assoc! temp k (m k)))
> (persistent! temp)))
>
> It returns {:a 1, :b 2, :c 3, :d 4, :e 5, :f 6, :g 7, :h 8}. The order is
> as I have defined, but there are *only 8 out of 10 items* in the new map.
>
> If I do the same with an atom, all items are taken into account, but the
> order is not as expected:
>
> (defn reorder-map-2 []
> (let [
> a (atom {})
> m {:j 10 :g 7 :b 2 :d 4 :e 5 :h 8 :i 9 :f 6 :c 3 :a 1 }
> kwds [:a :b :c :d :e :f :g :h :i :j]
> ]
> (doseq [k kwds]
> (swap! a assoc k (m k)))
> @a))
>
> It returns {:a 1, :c 3, :b 2, :f 6, :g 7, :d 4, :e 5, :j 10, :i 9, :h 8}
>
> I don't know the internals to judge in which order items are associated in
> a map. It seems that normal association prepends; transient association
> appends; atom association does not obey any particular order.
>
> Anyway,* it seems to be a bug in that the transient didn't accept more
> than 8 items*. It should, I suppose.
>
> Or am I doing sth. very wrong?
>
> Thank you -
>
>
>
>
>
>
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