Deduplicate code in scripts/helpers and test/helpers/iterate (#4895)

Co-authored-by: ernestognw <ernestognw@gmail.com>

test/helpers/iterate.js

@@ -1,15 +1,36 @@
-// Map values in an object
-const mapValues = (obj, fn) => Object.fromEntries(Object.entries(obj).map(([k, v]) => [k, fn(v)]));
-
-// Cartesian product of a list of arrays
-const product = (...arrays) => arrays.reduce((a, b) => a.flatMap(ai => b.map(bi => [...ai, bi])), [[]]);
-const unique = (...array) => array.filter((obj, i) => array.indexOf(obj) === i);
-const zip = (...args) =>
-  Array.from({ length: Math.max(...args.map(array => array.length)) }, (_, i) => args.map(array => array[i]));
-
 module.exports = {
-  mapValues,
-  product,
-  unique,
-  zip,
+  // ================================================= Array helpers =================================================
+
+  // Cut an array into an array of sized-length arrays
+  // Example: chunk([1,2,3,4,5,6,7,8], 3) → [[1,2,3],[4,5,6],[7,8]]
+  chunk: (array, size = 1) =>
+    Array.from({ length: Math.ceil(array.length / size) }, (_, i) => array.slice(i * size, i * size + size)),
+
+  // Cartesian cross product of an array of arrays
+  // Example: product([1,2],[a,b,c],[true]) → [[1,a,true],[1,b,true],[1,c,true],[2,a,true],[2,b,true],[2,c,true]]
+  product: (...arrays) => arrays.reduce((a, b) => a.flatMap(ai => b.map(bi => [...ai, bi])), [[]]),
+
+  // Range from start to end in increment
+  // Example: range(17,42,7) → [17,24,31,38]
+  range: (start, stop = undefined, step = 1) => {
+    if (!stop) {
+      stop = start;
+      start = 0;
+    }
+    return start < stop ? Array.from({ length: Math.ceil((stop - start) / step) }, (_, i) => start + i * step) : [];
+  },
+
+  // Unique elements, with an optional getter function
+  // Example: unique([1,1,2,3,4,8,1,3,8,13,42]) → [1,2,3,4,8,13,42]
+  unique: (array, op = x => x) => array.filter((obj, i) => array.findIndex(entry => op(obj) === op(entry)) === i),
+
+  // Zip arrays together. If some arrays are smaller, undefined is used as a filler.
+  // Example: zip([1,2],[a,b,c],[true]) → [[1,a,true],[2,b,undefined],[undefined,c,undefined]]
+  zip: (...args) => Array.from({ length: Math.max(...args.map(arg => arg.length)) }, (_, i) => args.map(arg => arg[i])),
+
+  // ================================================ Object helpers =================================================
+
+  // Create a new object by mapping the values through a function, keeping the keys
+  // Example: mapValues({a:1,b:2,c:3}, x => x**2) → {a:1,b:4,c:9}
+  mapValues: (obj, fn) => Object.fromEntries(Object.entries(obj).map(([k, v]) => [k, fn(v)])),
 };