feat:ChatGPT第 9 课：sortBy、sortWith、groupBy

src/main/scala/practise9/demo/Demo1SortBy.scala

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+package practise9.demo
+
+/*
+* 第 9 课：sortBy、sortWith、groupBy*/
+
+//sortBy 基础用法
+object Demo1SortBy {
+  def main(args: Array[String]): Unit = {
+    val nums = List(5, 2, 8, 1, 3)
+
+    val result = nums.sortBy(x => x)
+    val result2 = nums.sortBy(+_)
+
+    println(result)
+    println(result2)
+  }
+}

src/main/scala/practise9/demo/Demo2SortByProperty.scala

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+package practise9.demo
+
+/*
+* 按元组属性排序*/
+object Demo2SortByProperty {
+  def main(args: Array[String]): Unit = {
+    val students = List(
+      ("Tom", 80),
+      ("Jack", 95),
+      ("Alice", 70)
+    )
+    val result = students.sortBy(x => x._2)
+    println(result)
+  }
+}

src/main/scala/practise9/demo/Demo3SortByUnderscore.scala

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+package practise9.demo
+
+/*
+* sortBy 配合 _ */
+object Demo3SortByUnderscore {
+  def main(args: Array[String]): Unit = {
+    val students = List(
+      ("Tom", 80),
+      ("Jack", 95),
+      ("Alice", 70)
+    )
+    val result = students.sortBy(_._2)
+    println(result)
+  }
+}

src/main/scala/practise9/demo/Demo4SortByDescending.scala

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+package practise9.demo
+
+/*
+* sortBy 降序*/
+object Demo4SortByDescending {
+  def main(args: Array[String]): Unit = {
+    val nums = List(5, 2, 8, 1, 3)
+
+    // 默认升序
+    println(nums.sortBy(x => x))
+
+    val result = nums.sortBy(x => x).reverse
+    println(result)
+
+    // -_ 就是 x => -x
+    println(nums.sortBy(-_))
+  }
+}

src/main/scala/practise9/demo/Demo5SortWith.scala

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+package practise9.demo
+
+/*
+* sortWith 自定义比较*/
+object Demo5SortWith {
+  def main(args: Array[String]): Unit = {
+    val nums = List(5, 2, 8, 1, 3)
+
+    val result = nums.sortWith((a, b) => a > b)
+    /*
+    * a 和 b 比较
+    * ↓
+    * 如果 a > b
+    * ↓
+    * a 放前面*/
+
+    println(result)
+  }
+}

src/main/scala/practise9/demo/Demo6SortByAndSortWith.scala

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+package practise9.demo
+
+/*
+* sortBy 与 sortWith 区别*/
+object Demo6SortByAndSortWith {
+  def main(args: Array[String]): Unit = {
+    val students = List(
+      ("Tom", 80),
+      ("Jack", 95),
+      ("Alice", 70)
+    )
+
+    // 按照成绩排序
+    // 元素
+    //  ↓
+    // 提取一个排序依据
+    //  ↓
+    // 按照这个依据排序
+    println(students.sortBy(_._2).reverse)
+
+    // 比较两个学生的成绩
+    // ↓
+    // 决定谁排前面
+    println(students.sortWith((a, b) => a._2 > b._2))
+
+    //sortBy  → 按什么排序
+    //sortWith → 怎么比较
+  }
+
+}

src/main/scala/practise9/demo/Demo7GroupBy.scala

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+package practise9.demo
+
+/*
+* groupBy 基础用法*/
+object Demo7GroupBy {
+  def main(args: Array[String]): Unit = {
+    val nums = List(1, 2, 3, 4, 5, 6)
+
+    val result = nums.groupBy(x => x % 2)
+
+    println(result)
+  }
+}

src/main/scala/practise9/demo/Demo8GroupByStudentScore.scala

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+package practise9.demo
+
+/*
+* 按学生成绩分组*/
+object Demo8GroupByStudentScore {
+  def main(args: Array[String]): Unit = {
+    val students = List(
+      ("Tom", 85),
+      ("Jack", 92),
+      ("Alice", 76),
+      ("Bob", 88),
+      ("Lucy", 95)
+    )
+    val result = students.groupBy(student => {
+      val score = student._2
+
+      if (score >= 90) {
+        "优秀"
+      } else if (score >= 80) {
+        "良好"
+      } else {
+        "及格"
+      }
+    })
+
+    println(result)
+  }
+}

src/main/scala/practise9/demo/Demo9CollectionChain.scala

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+package practise9.demo
+
+/*
+* filter + map + sortBy 串联*/
+object Demo9CollectionChain {
+  def main(args: Array[String]): Unit = {
+    val nums = List(1, 2, 3, 4, 5, 6)
+
+    val result = nums
+      .filter(_ % 2 == 0)
+      .map(_ * 10)
+      .sortBy(+_)
+//      .sortBy(x => x)
+
+    println(result)
+  }
+}

src/main/scala/practise9/exercises/Exercises1.scala

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+package practise9.exercises
+/*
+* 练习 1：升序
+
+给：
+val nums = List(5, 2, 8, 1, 3)
+
+使用 sortBy，得到：
+List(1, 2, 3, 5, 8)*/
+object Exercises1 {
+  def main(args: Array[String]): Unit = {
+    val nums = List(5, 2, 8, 1, 3)
+    val result = nums.sortBy(+_)
+    println(result)
+  }
+}

src/main/scala/practise9/exercises/Exercises2.scala

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+package practise9.exercises
+/*
+* 练习 2：降序
+
+还是：
+
+val nums = List(5, 2, 8, 1, 3)
+
+使用 sortBy，得到：
+
+List(8, 5, 3, 2, 1)*/
+object Exercises2 {
+  def main(args: Array[String]): Unit = {
+      val nums = List(5, 2, 8, 1, 3)
+      val result = nums.sortBy(-_)
+      println(result)
+    }
+}

src/main/scala/practise9/exercises/Exercises3.scala

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+package practise9.exercises
+/*
+* 练习 3：学生成绩排序
+
+给：
+val students = List(
+  ("Tom", 80),
+  ("Jack", 95),
+  ("Alice", 70),
+  ("Bob", 85)
+)
+
+使用 sortBy 按成绩从低到高排序：
+(Alice,70)
+(Tom,80)
+(Bob,85)
+(Jack,95)
+
+提示：
+_._2*/
+object Exercises3 {
+  def main(args: Array[String]): Unit = {
+    val students = List(
+      ("Tom", 80),
+      ("Jack", 95),
+      ("Alice", 70),
+      ("Bob", 85)
+    )
+    val result = students.sortBy(_._2)
+    println(result)
+  }
+}

src/main/scala/practise9/exercises/Exercises4.scala

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+package practise9.exercises
+/*
+* 练习 4：sortWith
+还是上面的学生。
+
+使用 sortWith：
+按照成绩从高到低
+
+结果：
+List(
+  (Jack,95),
+  (Bob,85),
+  (Tom,80),
+  (Alice,70)
+)*/
+object Exercises4 {
+  def main(args: Array[String]): Unit = {
+    val students = List(
+      ("Tom", 80),
+      ("Jack", 95),
+      ("Alice", 70),
+      ("Bob", 85)
+    )
+    val result = students.sortWith((a, b) => a._2 > b._2)
+    println(result)
+  }
+}

src/main/scala/practise9/exercises/Exercises5.scala

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+package practise9.exercises
+/*
+* 练习 5：groupBy
+
+给：
+val nums = List(1, 2, 3, 4, 5, 6, 7, 8)
+
+按照奇偶分组：
+偶数 → List(2,4,6,8)
+奇数 → List(1,3,5,7)
+
+提示：
+groupBy(_ % 2)
+
+得到的 Map 的 Key 会是：
+0 → 偶数
+1 → 奇数*/
+object Exercises5 {
+  def main(args: Array[String]): Unit = {
+    val nums = List(1, 2, 3, 4, 5, 6, 7, 8)
+    val result = nums.groupBy(_ % 2)
+    println(result)
+  }
+}

src/main/scala/practise9/exercises/Exercises6.scala

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+package practise9.exercises
+/*
+* 练习 6 ⭐：成绩分组
+
+给：
+val students = List(
+  ("Tom", 85),
+  ("Jack", 92),
+  ("Alice", 76),
+  ("Bob", 88),
+  ("Lucy", 95),
+  ("Mike", 60)
+)
+
+按照成绩分成：
+优秀：>= 90
+良好：>= 80
+及格：>= 60
+
+最终类似：
+优秀 → Jack, Lucy
+良好 → Tom, Bob
+及格 → Alice, Mike
+
+要求使用：
+groupBy*/
+object Exercises6 {
+  def main(args: Array[String]): Unit = {
+    val students = List(
+      ("Tom", 85),
+      ("Jack", 92),
+      ("Alice", 76),
+      ("Bob", 88),
+      ("Lucy", 95),
+      ("Mike", 60)
+    )
+    val result = students.groupBy(student => {
+      if (student._2 >= 90) {
+        "优秀"
+      }else if (student._2 >=80){
+        "良好"
+      }else if (student._2 >=60){
+        "及格"
+      }else "不及格"
+    })
+    println(result)
+  }
+}
+

src/main/scala/practise9/exercises/Exercises7.scala

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+package practise9.exercises
+/*
+* 练习 7 ⭐⭐ 综合题
+
+给：
+val students = List(
+  ("Tom", 85),
+  ("Jack", 92),
+  ("Alice", 76),
+  ("Bob", 88),
+  ("Lucy", 95),
+  ("Mike", 60)
+)
+
+完成：
+1. filter：去掉不及格成绩（< 60）
+2. sortBy：按照成绩从高到低
+3. map：只保留学生姓名
+
+最终：
+List(Lucy, Jack, Bob, Tom, Alice, Mike)*/
+object Exercises7 {
+  def main(args: Array[String]): Unit = {
+    val students = List(
+      ("Tom", 85),
+      ("Jack", 92),
+      ("Alice", 76),
+      ("Bob", 88),
+      ("Lucy", 95),
+      ("Mike", 60)
+    )
+    val result = students
+      .filter(_._2 >= 60)
+      .sortBy(-_._2)
+      .map(_._1)
+
+    println(result)
+
+  }
+}