From 80ddb5746860c5615c84670659ee03aa93e68bc9 Mon Sep 17 00:00:00 2001
From: Roman Dvornov <rdvornov@gmail.com>
Date: Sat, 18 May 2024 20:30:04 +0200
Subject: [PATCH] Fixed group() method to not omit elements with an empty array
 as key

---
 CHANGELOG.md          |  3 ++-
 src/methods.js        | 10 ++++++++--
 test/methods/group.js | 38 ++++++++++++++++++++++++++++++++------
 3 files changed, 42 insertions(+), 9 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ee0470d..c257952 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,7 +2,8 @@
 
 - Added support for TypedArray in bracket notation, filtering, mapping, matching, spread operator, +/- operators
 - Changed `is array` assertion to return `true` for TypedArray values
-- Fixed `lastIndexOf()` behavior when `fromIndex` is zero; previously, the search incorrectly started from the end of an array instead of the zero position
+- Fixed `lastIndexOf()` method behavior when `fromIndex` is zero; previously, the search incorrectly started from the end of an array instead of the zero position
+- Fixed `group()` method to include elements with an empty array as a key in the group with `key: undefined`; previously, such elements were omitted from the result
 - Modified the behavior of slice notation:
     - When the value is a string, the result remains a string (was an array of chars)
     - When `from` is greater than `to` and `step` is not specified, `step` defaults to `-1` (i.e. `$[3:1]` is the same as `$[1:3:-1]`)
diff --git a/src/methods.js b/src/methods.js
index 26adc16..b0bf528 100644
--- a/src/methods.js
+++ b/src/methods.js
@@ -161,8 +161,14 @@ export default Object.freeze({
             const keys = keyGetter(item);
 
             if (Array.isArray(keys)) {
-                for (const key of keys) {
-                    addToMapSet(map, key, valueGetter(item));
+                if (keys.length > 0) {
+                    const value = valueGetter(item);
+
+                    for (const key of keys) {
+                        addToMapSet(map, key, value);
+                    }
+                } else {
+                    addToMapSet(map, undefined, valueGetter(item));
                 }
             } else {
                 addToMapSet(map, keys, valueGetter(item));
diff --git a/test/methods/group.js b/test/methods/group.js
index e81ef0f..91ff8eb 100644
--- a/test/methods/group.js
+++ b/test/methods/group.js
@@ -42,13 +42,39 @@ describe('group()', () => {
     });
 
     it('should group by an element when key value is an array', () => {
+        const data = [
+            { id: 1, tags: ['foo', 'bar'] },
+            { id: 2, tags: ['baz'] },
+            { id: 3, tags: ['bar', 'baz'] },
+            { id: 4, tags: ['bar'] }
+        ];
+
         assert.deepEqual(
-            query('.group(=>refs.type)')(data),
-            ['svg', 'css', 'js']
-                .map(type => ({
-                    key: type,
-                    value: data.filter(item => item.refs.find(ref => ref.type === type))
-                }))
+            query('group(=>tags)')(data),
+            [
+                { key: 'foo', value: [data[0]] },
+                { key: 'bar', value: [data[0], data[2], data[3]] },
+                { key: 'baz', value: [data[1], data[2]] }
+            ]
+        );
+    });
+
+    it('should not loose elements with empty array', () => {
+        const data = [
+            { id: 1, tags: ['foo', 'bar'] },
+            { id: 2, tags: ['baz'] },
+            { id: 3, tags: ['bar', 'baz'] },
+            { id: 4, tags: [] }
+        ];
+
+        assert.deepEqual(
+            query('group(=>tags)')(data),
+            [
+                { key: 'foo', value: [data[0]] },
+                { key: 'bar', value: [data[0], data[2]] },
+                { key: 'baz', value: [data[1], data[2]] },
+                { key: undefined, value: [data[3]] }
+            ]
         );
     });
 });