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@cgrand cgrand/gist:4655215 forked from anonymous/gist:4655172
Last active Dec 11, 2015

What would you like to do?
cheap merge-with when you only need lookup
(defn cheap-merge-with
"Merges two maps-as-functions" [f a b]
(memoize (fn this
([k] (this k nil))
([k default]
(let [av (a k this)
bv (b k this)]
(if (identical? this av)
(if (identical? this bv)
(if (identical? this bv)
(f av bv))))))))
(defn fold-vec-maps-into-map [coll]
"Provided a reducer, concatenate into a vector.
Note: same as (into [] coll), but parallel."
(let [merge-fn (partial cheap-merge-with into)]
(r/fold (r/monoid merge-fn hash-map) merge-fn coll)))
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