feat(arrays): add selectThresholdMin/Max() fns

packages/arrays/src/threshold.ts

@@ -0,0 +1,57 @@
+/**
+ * Higher order function. Takes an object of threshold values and their target
+ * values, as well as a default value. Returns a new function which then matches
+ * a given value against all given thresholds and returns a matching target
+ * value, of (if none matched), the given default.
+ *
+ * @remarks
+ * The thresholds will be sorted & matched in ascending order using `<=`
+ * comparison.
+ *
+ * @example
+ * ```ts
+ * const numColumns = selectThresholdMin({ 480: 1, 640: 2, 960: 3 }, 4);
+ *
+ * numColumns(320) // 1
+ *
+ * numColumns(481) // 2
+ *
+ * numColumns(768) // 3
+ *
+ * numColumns(1024) // 4
+ * ```
+ *
+ * @param thresholds
+ * @param defaultVal
+ */
+export const selectThresholdMin = <T>(
+	thresholds: Record<number, T>,
+	defaultVal: T
+) => {
+	const $thresholds = Object.entries(thresholds)
+		.map(([k, v]) => <[number, T]>[+k, v])
+		.sort((a, b) => a[0] - b[0]);
+	return (x: number) => {
+		const res = $thresholds.find((t) => x <= t[0]);
+		return res ? res[1] : defaultVal;
+	};
+};
+
+/**
+ * Similar to {@link selectThresholdMin}, but uses `>=` ordering.
+ *
+ * @param thresholds
+ * @param defaultVal
+ */
+export const selectThresholdMax = <T>(
+	thresholds: Record<number, T>,
+	defaultVal: T
+) => {
+	const $thresholds = Object.entries(thresholds)
+		.map(([k, v]) => <[number, T]>[+k, v])
+		.sort((a, b) => b[0] - a[0]);
+	return (x: number) => {
+		const res = $thresholds.find((t) => x >= t[0]);
+		return res ? res[1] : defaultVal;
+	};
+};