• (project xrel ks)
Returns a rel of the elements of xrel with only the keys in ks

1 Example top

  • ;; `project` strips out unwanted key/value pairs from a set of maps. 
    ;; Suppose you have these descriptions of cows:
    user=> (def cows #{  {:name "betsy" :id 33} {:name "panda" :id 34} })
    ;; You care only about the names. So you can get them like this:
    user=> (project cows [:name])
    #{{:name "panda"} {:name "betsy"}}
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Plus_12x12 Minus_12x12 Source clojure/set.clj:71 top

(defn project
  "Returns a rel of the elements of xrel with only the keys in ks"
  {:added "1.0"}
  [xrel ks]
    (set (map #(select-keys % ks) xrel)))
Vars in clojure.set/project:
Used in 0 other vars

Comments top

3 comment(s) for project.

is there a function that is like project, but returns a set of hash-maps with with all the keys but the ones project was given?

This doesn't exist in clojure.set, but I think it would be what you wanted.

(defn project-not [xrel ks]
  ;; convert the given key sequence into a hash-set
  ;; This represents keys that you don't want included
  (let [ks-set (into #{} ks)]
    ;; Do a projection on the keys that are not in ks
    (clojure.set/project xrel
                         ;; Assumes xrel is a set of maps
                         ;; Grab the first map and extract the keys
                         ;; Then remove any keys that are in ks-set
                         ;; This will leave the remaining keys for
                         ;; projection
                         (remove #(ks-set %) (keys (first xrel))))))

user> (project-not cows [:id])
#{{:name "panda" {:name "betsy"}}

it strikes me as being very odd that the key set is a vector as opposed to vargs

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