fix: daia availability

src/app/_helpers/collections/group-by.spec.ts

@@ -13,7 +13,7 @@
  *  this program. If not, see <https://www.gnu.org/licenses/>.
  */
 
-import {groupBy, groupByProperty} from './group-by';
+import {groupBy, groupByStable, groupByProperty} from './group-by';
 
 describe('groupBy', () => {
   it('should group an array by a key', () => {
@@ -77,6 +77,29 @@ describe('groupBy', () => {
   });
 });
 
+describe('groupByStable', () => {
+  const array = [
+    {id: 2, name: 'two'},
+    {id: 4, name: 'three'},
+    {id: 3, name: 'three'},
+    {id: 1, name: 'one'},
+  ];
+  const result = groupByStable(array, it => it.name);
+
+  it('should group an array by keys', () => {
+    expect(result.get('one')).toEqual([{id: 1, name: 'one'}]);
+    expect(result.get('two')).toEqual([{id: 2, name: 'two'}]);
+    expect(result.get('three')).toEqual([
+      {id: 4, name: 'three'},
+      {id: 3, name: 'three'},
+    ]);
+  });
+
+  it('should provide ordered keys', () => {
+    expect([...result.keys()]).toEqual(['two', 'three', 'one']);
+  });
+});
+
 describe('groupByProperty', function () {
   it('should group by property', () => {
     const array = [

src/app/_helpers/collections/group-by.ts

@@ -28,6 +28,21 @@ export function groupBy<T>(
   }, {});
 }
 
+/**
+ * Group an array by a function (returns a Map, whose keys keep order info of items entry)
+ */
+export function groupByStable<T>(
+  collection: T[],
+  group: (item: T) => string | undefined,
+): Map<string, T[]> {
+  return collection.reduce((accumulator: Map<string, T[]>, item) => {
+    const key = group(item) ?? '';
+    accumulator.set(key, accumulator.get(key) ?? []);
+    accumulator.get(key)?.push(item);
+    return accumulator;
+  }, new Map<string, T[]>());
+}
+
 /**
  *
  */