clojure.set/union

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Type: function Added: Clojure 1.0 Examples: 6 Runnable: 0

([] [s1] [s1 s2] [s1 s2 & sets])

Return a set that is the union of the input sets

Examples

by Brian Marick on 2010-07-13 . May have evaluation errors. ▶

(union) #{} (union #{1 2}) #{1 2} (union #{1 2} #{2 3}) #{1 2 3} (union #{1 2} #{2 3} #{3 4}) #{1 2 3 4}

by sleyzerzon on 2016-08-13 . May have evaluation errors. ▶

(reduce (fn [flattened [key val]] (conj flattened val)) #{} {:e #{:m :f}, :c #{:f}, :b #{:c :f}, :d #{:m :f}, :a #{:c :f}}) ;;=> #{#{:m :f} #{:c :f} #{:f}} (reduce (fn [flattened [key val]] (clojure.set/union flattened val)) #{} {:e #{:m :f}, :c #{:f}, :b #{:c :f}, :d #{:m :f}, :a #{:c :f}}) ;;=> #{:m :c :f}

by sleyzerzon on 2016-08-13 . May have evaluation errors. ▶

(defn flatten-dpdnts [dpdnts-map] (apply set/union (vals dpdnts-map))) (flatten-dpdnts {:e #{:m :f}, :c #{:f}, :b #{:c :f}, :d #{:m :f}, :a #{:c :f}}) ;;=> #{:m :c :f}

by jafingerhut on 2018-07-27 . May have evaluation errors. ▶

;; Advice: Do not call union with non-set arguments. If you are ;; concerned that you may be unintentionally doing so, and want an ;; exception to be thrown if you do, consider using the library ;; funjible (https://github.com/jafingerhut/funjible) which provides ;; its own definition of union that is identical to Clojure's, except ;; it checks the types of its arguments. ;; union might or might not return what you expect if you give it ;; values that are not sets. The implementation of union _does not ;; check_ whether you are actually giving it values that are sets. It ;; _assumes_ so. ;; This looks like what someone might expect. It _happens_ to give ;; back the same answer as if you coerced the second argument to a ;; set. (union #{1 2 3} [4 5]) #{1 4 3 2 5} ;; Wait, this returned a vector, not a set! (union #{1 2} [3 4 5]) [3 4 5 1 2] ;; This also returned a vector, and some elements are duplicates of ;; each other! (union #{1 2} [3 4 5] #{4 5}) [3 4 5 1 2 4 5] ;; Why not change the definition of union so it throws an exception if ;; you give it a non-set argument? I would guess that the primary ;; reason is that the extra run-time type checks would slow union down ;; by an amount that the Clojure core team does not want everyone to ;; have to pay on every such call. ;; Related Clojure tickets: ;; https://dev.clojure.org/jira/browse/CLJ-1953 ;; https://dev.clojure.org/jira/browse/CLJ-2287

by timgilbert on 2018-12-17 . May have evaluation errors. ▶

;; (set/union) treats nil as the empty set, as you'd probably expect. (clojure.set/union nil #{1 2} nil) ;;=> #{1 2} ;; This makes it handy to use as an accumulator in combination with (update-in): (update-in {} [:a :b :c] clojure.set/union #{333}) ;;=> {:a {:b {:c #{333}}}}

by reborg on 2020-03-05 . May have evaluation errors. ▶

;; The "powerset" is the set of all the combinations of "items" (require '[clojure.set :refer [union]]) (defn powerset [items] (reduce (fn [s x] (union s (map #(conj % x) s))) (hash-set #{}) items)) (powerset #{1 2 3}) ;; #{#{} #{3} #{2} #{1} #{1 3 2} #{1 3} #{1 2} #{3 2}}

See also

• clojure.set/intersection (0)
• clojure.set/difference (0)
• clojure.set/superset?

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