On Wed, Jan 19, 2011 at 11:23 PM, Stefan Rohlfing
<stefan.rohlf...@gmail.com> wrote:
> Hi all,
>
> I tried another implementation of 'merge-with' using nested calls to
> 'reduce'. However,
> I just cannot get it to work correctly:
>
> (defn my-merge-with [f & maps]
> (when (some identity
> maps)
> (reduce
> (fn [acc m]
> (reduce
> (fn [_ [key val]]
> (assoc acc key (if-let [old-val (get acc key)]
> (f old-val val)
> val)))
> {} m))
> {} maps)))
To me, it looks like you're throwing away some results. (assoc acc
key val) creates a new map with the updated key, it doesn't update the
old one in-place.
Perhaps something like:
(defn my-merge-with [f & maps]
(when (some identity maps)
(reduce
(fn [acc m]
(reduce
(fn [acc2 [key val]]
(assoc acc2 key (if-let [old-val (get acc2 key)]
(f old-val val)
val)))
acc m))
{} maps)))
-John
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