feat(random): add randomID() & weightedRandom()

packages/random/src/index.ts

@@ -4,3 +4,6 @@ export * from "./system";
 export * from "./xorshift128";
 export * from "./xorwow";
 export * from "./xsadd";
+
+export * from "./random-id";
+export * from "./weighted-random";

packages/random/src/random-id.ts

@@ -0,0 +1,28 @@
+import { IRandom } from "./api";
+import { SYSTEM } from "./system";
+
+/**
+ * Generates and returns a random string of `len` characters (default
+ * 4), plus optional given `prefix` and using only provided `syms`
+ * characters (default lowercase a-z).
+ *
+ * ```
+ * randomID()
+ * "qgdt"
+ *
+ * randomID(8, "id-", "0123456789ABCDEF")
+ * "id-94EF6E1A"
+ * ```
+ *
+ * @param len
+ * @param prefix
+ * @param syms
+ * @param rnd
+ */
+export const randomID =
+    (len = 4, prefix = "", syms = "abcdefghijklmnopqrstuvwxyz", rnd: IRandom = SYSTEM) => {
+        for (const n = syms.length; --len >= 0;) {
+            prefix += syms[rnd.float(n) | 0];
+        }
+        return prefix;
+    };

packages/random/src/weighted-random.ts

@@ -0,0 +1,40 @@
+import { IRandom } from "./api";
+import { SYSTEM } from "./system";
+
+/**
+ * Returns a no-arg function which produces a random choice of given
+ * weighted `choices` and using given `IRandom` instance (default:
+ * `SYSTEM`). If `weights` are given, it must be the same size as
+ * `choices`. If omitted, each choice will have same probability.
+ *
+ * https://www.electricmonk.nl/log/2009/12/23/weighted-random-distribution/
+ *
+ * @param choices
+ * @param weights
+ */
+export const weightedRandom = <T>(
+    choices: Array<T>,
+    weights?: ArrayLike<number>,
+    rnd: IRandom = SYSTEM
+) => {
+    const opts = choices.map(
+        weights ?
+            (x, i) => <[T, number]>[x, weights[i]] :
+            (x) => <[T, number]>[x, 1]
+    ).sort((a, b) => b[1] - a[1]);
+    const n = choices.length;
+    let total = 0, i: number, r: number, sum: number;
+    for (i = 0; i < n; i++) {
+        total += opts[i][1];
+    }
+    return () => {
+        r = rnd.float(total);
+        sum = total;
+        for (i = 0; i < n; i++) {
+            sum -= opts[i][1];
+            if (sum <= r) {
+                return opts[i][0];
+            }
+        }
+    };
+};