feat(arrays): add argMin()/argMax()

packages/arrays/src/argmin.ts

@@ -0,0 +1,53 @@
+import type { Predicate2 } from "@thi.ng/api";
+
+/**
+ * Takes an array of numbers and returns the index of the item which is
+ * considered the minimum value according to the given initial `min` value
+ * (default: ∞) and predicate (both optional). Returns -1 if `items` is empty.
+ *
+ * @remarks
+ * See {@link argMax}.
+ *
+ * @example
+ * ```ts
+ * argMin([42, 11, 66, 23])
+ * // 1
+ *
+ * // same as argmax() with defaults
+ * argMin([42, 11, 66, 23], -Infinity, (a, b) => a > b)
+ * // 2
+ * ```
+ *
+ * @param buf
+ * @param min
+ * @param pred
+ */
+export const argMin = (
+	buf: ArrayLike<number>,
+	min = Infinity,
+	pred: Predicate2<number> = (a, b) => a < b
+) => {
+	let id = -1;
+	for (let i = 0, n = buf.length; i < n; i++) {
+		const x = buf[i];
+		if (pred(x, min)) {
+			min = x;
+			id = i;
+		}
+	}
+	return id;
+};
+
+/**
+ * Similar to {@link argMin}, but selects index of maximum item. Returns -1 if
+ * `items` is empty.
+ *
+ * @param items
+ * @param min
+ * @param pred
+ */
+export const argMax = (
+	items: ArrayLike<number>,
+	min = -Infinity,
+	pred: Predicate2<number> = (a, b) => a > b
+) => argMin(items, min, pred);