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jeroenvandijk/group_by.clj

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Last active October 1, 2015 07:56
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group-by as a transducer
Raw
group_by.clj
(defn group-by
([f]
(fn [rf]
(let [grouped-value (volatile! (transient {}))]
(fn
([] (rf))
([result]
(rf result (persistent! @grouped-value)))
([result input]
(let [key (f input)]
(vswap! grouped-value assoc! key (conj (get @grouped-value key []) input))
result))))))
([f coll]
(into {} (group-by f) coll)))
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