groupingBy using Classifier, DownStream

spdpiyush · spdpiyush · commit fb29eb255972 · 2025-03-07T15:45:27.000+05:30
diff --git a/Modern-Java-Examples/src/com/learn/streams_terminal/StreamsGroupingByExample.java b/Modern-Java-Examples/src/com/learn/streams_terminal/StreamsGroupingByExample.java
@@ -29,6 +29,9 @@ public static void main(String[] args) {
 
         System.out.println("Student grouped based on Gender : " + groupingByExample1());
         System.out.println("Student grouped based on PASS/FAIL : " + groupingByExample2());
+
+        System.out.println("Two Level Grouping : " + twoLevelGrouping1());
+        System.out.println("Two Level Grouping " + twoLevelGrouping2());
     }
 
     /**
@@ -54,4 +57,26 @@ public static Map<String, List<Student>> groupingByExample2() {
                 .stream()
                 .collect(Collectors.groupingBy(student -> student.getGpa() >= 3.8 ? "PASS" : "FAIL"));
     }
+
+    /**
+     * <p>
+     *     Here, we are performing 2 Level grouping.
+     *     First Grouping is at the Grade Level.
+     *     Second Grouping is at  a customized implementation (i.e. based on PASS ond FAIL ) on GPA.
+     * </p>
+     */
+    public static Map<Integer, Map<String, List<Student>>> twoLevelGrouping1() {
+        return StudentDataBase.getAllStudents()
+                .stream()
+                .collect(Collectors.groupingBy(Student::getGradeLevel,
+                        Collectors.groupingBy(student -> student.getGpa() >= 3.8 ? "PASS" : "FAIL")));
+    }
+
+
+    public static Map<Integer, Integer> twoLevelGrouping2() {
+        return StudentDataBase.getAllStudents()
+                .stream()
+                .collect(Collectors.groupingBy(Student::getGradeLevel,
+                        Collectors.summingInt(Student::getNoteBooks)));
+    }
 }
diff --git a/README.md b/README.md
@@ -49,7 +49,6 @@ This repository contains the basic &amp; advance level examples related to Java
     * [ minBy() and maxBy()](Modern-Java-Examples/src/com/learn/streams_terminal/StreamsMinByMaxByExample.java)
     * [ summingInt() and averagingInt()](Modern-Java-Examples/src/com/learn/streams_terminal/StreamsSumAvgExample.java)
     * [ groupingBy()](Modern-Java-Examples/src/com/learn/streams_terminal/StreamsGroupingByExample.java)
-    
 
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