f/matej-utils - add: numberComparator

packages/ts-utils/src/sort.ts

@@ -0,0 +1,41 @@
+/**
+ * Maps an element of an array to a number and returns a function 
+ * that compares the number value of two values.
+ *
+ * Call this and pass the result into the .sort function.
+ *
+ * The array gets sorted in such a way that the elements get sorted
+ * by the number they map to.
+ *
+ * So the higher the number, the later in the array the element will be.
+ *
+ * If the number is same, the order is kept the same (.sort uses a stable sorting algorithm)
+ *
+ * Especially useful when you need
+ * - to push some items to the front (for example user's favorite item)
+ * - other items to the back (for example inactive items)
+ * - keep the order of the other items the same
+ *
+ * @example
+ * ```
+ * const arr = ['alpha', 'beta', 'gamma']
+ *
+ * const userFavoriteGreekLetter = 'gamma'
+ *
+ * // we want to push the favorite greek letter to the front
+ * arr.sort(numberComparator(x => x === userFavoriteGreekLetter ? -1 : 0))
+ *
+ * // prints "gamma, alpha, beta"
+ * console.log(arr.join(', '))
+ * ```
+ */
+export function numberComparator<T>(
+  map: (x: T) => number
+): (p: T, n: T) => number {
+  return (p: T, n: T): number => {
+    const pNumber = map(p);
+    const nNumber = map(n);
+
+    return pNumber - nNumber;
+  };
+}