refactor: improve group challenges and add clearer aggregation hints

Author: ricardohsmello

java/104_aggregation_pipeline_group_by.ipynb

@@ -47,6 +47,8 @@
     "\n",
     "import static com.mongodb.client.model.Sorts.descending;\n",
     "import static com.mongodb.client.model.Aggregates.limit;\n",
+    "import static com.mongodb.client.model.Aggregates.group;\n",
+    "import static com.mongodb.client.model.Aggregates.sort;\n",
     "\n",
     "import org.bson.Document;\n",
     "import java.util.Arrays;\n",
@@ -69,7 +71,8 @@
     "}\n",
     "\n",
     "MongoDatabase library = mongoClient.getDatabase(\"library\");\n",
-    "MongoCollection<Document> books = library.getCollection(\"books\");"
+    "MongoCollection<Document> books = library.getCollection(\"books\");\n",
+    "MongoCollection<Document> reviews = library.getCollection(\"reviews\");\n"
    ]
   },
   {
@@ -118,7 +121,10 @@
    "id": "d96043ab",
    "metadata": {},
    "source": [
-    "### 1. Find the average book rating of all books\n",
+    "### 1. Find the average rating for each book\n",
+    "\n",
+    "Hint: use the `reviews` collection, group by `bookId`, and calculate the average of the `rating` field.\n",
+    "\n",
     "[Solution here](https://mongodb-developer.github.io/sql-to-query-api-lab/docs/aggregation/group#-1-find-the-average-book-rating-of-all-books)"
    ]
   },
@@ -129,15 +135,27 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "// type your code here"
+    "// TYPE YOUR CODE HERE\n",
+    "\n",
+    "AggregateIterable<Document> result = reviews.aggregate(\n",
+    "    List.of(\n",
+    "        <REPLACE_WITH_GROUP_STAGE>\n",
+    "    )\n",
+    ");\n",
+    "\n",
+    "for (Document doc : result) {\n",
+    "    System.out.println(\"result: \" + doc.toJson());\n",
+    "}"
    ]
   },
   {
    "cell_type": "markdown",
    "id": "2b9bb53e",
    "metadata": {},
    "source": [
-    "### 2. Find users with the most number of reviews (Hint: use sum + sort)\n",
+    "### 2. Find the top 5 users with the highest number of reviews - use (Sort + Sum)\n",
+    "Hint: use `sum` + `sort` to count and order the results, and don’t forget to use `limit` to keep the output easier to inspect.\n",
+    "\n",
     "[Solution here](https://mongodb-developer.github.io/sql-to-query-api-lab/docs/aggregation/group#-2-find-users-with-the-most-number-of-reviews-hint-use-the-name-field-in-the-reviews-collection)"
    ]
   },
@@ -148,16 +166,28 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "// type your code here"
+    "AggregateIterable<Document> result = reviews.aggregate(\n",
+    "    List.of(\n",
+    "        <REPLACE_WITH_GROUP_STAGE>                        \n",
+    "        <REPLACE_WITH_LIMIT_STAGE>\n",
+    "    )\n",
+    ");\n",
+    "\n",
+    "for (Document doc : result) {\n",
+    "    System.out.println(\"user: \" + doc.toJson());\n",
+    "}"
    ]
   },
   {
    "cell_type": "markdown",
    "id": "74e33d58",
    "metadata": {},
    "source": [
-    "### 3. Find users with the most number of reviews (Hint: use $sortByCount)\n",
-    "[Solution here](https://mongodb-developer.github.io/sql-to-query-api-lab/docs/aggregation/group#-2-find-users-with-the-most-number-of-reviews-hint-use-the-name-field-in-the-reviews-collection)"
+    "### 3. Find the top 5 users with the highest number of reviews - use (SortByCount)\n",
+    "\n",
+    "Hint: use `sortByCount` with the `name` field, and remember to use `$limit` to keep the output easier to inspect.\n",
+    "\n",
+    "[Solution here](https://mongodb-developer.github.io/sql-to-query-api-lab/docs/aggregation/group#-2-find-users-with-the-most-number-of-reviews-hint-use-the-name-field-in-the-reviews-collection)\n"
    ]
   },
   {
@@ -167,7 +197,18 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "// type your code here"
+    "// TYPE YOUR CODE HERE\n",
+    "\n",
+    "AggregateIterable<Document> result = reviews.aggregate(\n",
+    "    List.of(\n",
+    "        <REPLACE_WITH_SORT_BY_COUNT_STAGE>,\n",
+    "        <REPLACE_WITH_LIMIT_STAGE>\n",
+    "    )\n",
+    ");\n",
+    "\n",
+    "for (Document doc : result) {\n",
+    "    System.out.println(\"user: \" + doc.toJson());\n",
+    "}"
    ]
   }
  ],