Generate random numbers without repeating a value: Difference between revisions

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 [19, 15, 10, 6, 17, 13, 14, 9, 2, 20, 3, 18, 8, 16, 7, 12, 1, 4, 5, 11]
 </pre>
+=={{header|JavaScript}}==
+<lang javascript>(() => {
+    "use strict";
+    // ---------- NON-REPEATING RANDOM NUMBERS -----------
+    // main :: IO ()
+    const main = () =>
+        sortOn(Math.random)(
+            enumFromTo(1)(20)
+        );
+    // --------------------- GENERIC ---------------------
+    // comparing :: (a -> b) -> (a -> a -> Ordering)
+    const comparing = f =>
+        // The ordering of f(x) and f(y) as a value
+        // drawn from {-1, 0, 1}, representing {LT, EQ, GT}.
+        x => y => {
+            const
+                a = f(x),
+                b = f(y);
+            return a < b ? -1 : (a > b ? 1 : 0);
+        };
+    // enumFromTo :: Int -> Int -> [Int]
+    const enumFromTo = m =>
+        n => Array.from({
+            length: 1 + n - m
+        }, (_, i) => m + i);
+    // sortBy :: (a -> a -> Ordering) -> [a] -> [a]
+    const sortBy = f =>
+        // A copy of xs sorted by the comparator function f.
+        xs => xs.slice()
+        .sort((a, b) => f(a)(b));
+    // sortOn :: Ord b => (a -> b) -> [a] -> [a]
+    const sortOn = f =>
+        // Equivalent to sortBy(comparing(f)), but with f(x)
+        // evaluated only once for each x in xs.
+        // ('Schwartzian' decorate-sort-undecorate).
+        xs => sortBy(
+            comparing(x => x[0])
+        )(
+            xs.map(x => [f(x), x])
+        )
+        .map(x => x[1]);
+    // MAIN ---
+    return JSON.stringify(main());
+})();</lang>
+{{Out}}
+For example:
+<pre>[6,9,8,16,5,15,19,7,13,12,4,20,1,2,18,11,14,17,10,3]</pre>
 =={{header|jq}}==