distinct on sha.clj

(defn versions-to-fetch [local remote]
  (let [versions-missing (second (diff local remote))]
    (->> versions-missing
         (map #(with-meta (select-keys % [:sha]) %))
         set
         (map meta)
         set)))

(def data
#{{:date "2014-12-08T18:44:53.846-00:00", :id 1, :location "apps/version1.js", 
:sha "0760efcd391bc59b34fbdbc24749543b6dfea1e9d746c7885d3014d3c724a5dd"} 
{:date "2014-12-08T18:44:53.846-00:00", :id 2, :location "apps/version1.js", 
:sha "0760efcd391bc59b34fbdbc24749543b6dfea1e9d746c7885d3014d3c724a5dd"} 
{:date "2014-12-08T18:44:53.846-00:00", :id 3, :location "apps/version1.js", 
:sha "0760efcd391bc59b34fbdbc24749543b6dfea1e9d746c7885d3014d3c724a5dd"} 
{:date "2014-12-08T18:44:53.846-00:00", :id 4, :location "apps/version1.js", 
:sha "0760efcd391bc59b34fbdbc24749543b6dfea1e9d746c7885d3014d3c724a5dd"}})

(versions-to-fetch #{} data)

;;output
;;#{{:date "2014-12-08T18:44:53.846-00:00", :id 1, :location "apps/version1.js", :sha "0760efcd391bc59b34fbdbc24749543b6dfea1e9d746c7885d3014d3c724a5dd"}}