shuffle takes a collection and returns a vector containing a random permutation of its elements. It is useful when every element should appear once in randomized order rather than selecting one element repeatedly. section 8.3.2 section 8.3.1
The contract is straightforward, with important input restrictions:
- Accepts most Clojure collections, but excludes maps, transients, native arrays, and nil. section 8.3.2
- Returns a vector, regardless of the supported collection type supplied. section 8.3.2
- Can raise ClassCastException for unsupported collection interfaces and NullPointerException for nil. section 8.3.2
- Uses Fisher–Yates shuffling supplied through the Java JDK. section 8.3.2
Randomize hosts before round-robin use
(defn round-robin [f hosts] (let [hosts (shuffle hosts) idx (atom 0)] (fn [] (f (nth hosts @idx)) (reset! idx (mod (inc @idx) (count hosts)))))) (def hosts ["10.100.89.42" "10.100.86.57" "10.100.23.12"]) (def get-host (round-robin request hosts)) (get-host) ;; calling http://10.100.23.12/index.html section 8.3.2
Use rand-nth when one random element is needed; use shuffle when multiple sequential selections should avoid retrieving the same element twice. section 8.3.1
Listing 8.11. → Random Selection, Random Permutation, Collection Shuffle
(shuffle [coll])
Browse the concise function listing for shuffle. section 8.3.2
