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半夏orz
发表于 2020-8-30 22:50
public class groupingBy {
public static void main(String[] args) {
ArrayList<Student> list = new ArrayList<>();
list.add(new Student("王一", 21, "11", 1, new BigDecimal("193.0"), Timestamp.valueOf(LocalDateTime.now()), Timestamp.valueOf(LocalDateTime.now().plusMinutes(15L))));
list.add(new Student("郑二", 22, "22", 0, new BigDecimal("171.0"), Timestamp.valueOf(LocalDateTime.now()), Timestamp.valueOf(LocalDateTime.now().plusHours(16L))));
list.add(new Student("张三", 23, "33", 1, new BigDecimal("180.1"), Timestamp.valueOf(LocalDateTime.now()), Timestamp.valueOf(LocalDateTime.now().plusSeconds(500L))));
list.add(new Student("李四", 24, "44", 0, new BigDecimal("183.2"), Timestamp.valueOf(LocalDateTime.now()), Timestamp.valueOf(LocalDateTime.now().plusMinutes(18L))));
list.add(new Student("赵五", 25, "55", 1, new BigDecimal("178.3"), Timestamp.valueOf(LocalDateTime.now()), Timestamp.valueOf(LocalDateTime.now().plusMinutes(13L))));
list.add(new Student("韩六", 26, "88", 0, new BigDecimal("169.4"), Timestamp.valueOf(LocalDateTime.now()), Timestamp.valueOf(LocalDateTime.now().plusMinutes(1L))));
list.add(new Student("田七", 27, "77", 1, new BigDecimal("173.5"), Timestamp.valueOf(LocalDateTime.now()), Timestamp.valueOf(LocalDateTime.now().plusMinutes(17L))));
list.add(new Student("卢八", 28, "88", 0, new BigDecimal("159.6"), Timestamp.valueOf(LocalDateTime.now()), Timestamp.valueOf(LocalDateTime.now().plusMinutes(1L))));
// list.add(new Student("钱九", 29, null, 1, new BigDecimal("180.1")));
// list.add(new Student("魏十", null, "99", null, null));
// list.add(new Student("肖十一", null, "", null, null));
// list.add(new Student("柘十二", null, null, null, null));
//1根据性别进行分组
//1.1 为null的数据不需要，直接过滤
Map<Integer, List<Student>> collect = list.stream()
.filter(a -> a.getGender() != null)
.collect(Collectors.groupingBy(Student::getGender));
//1.2 需要保留为null的数据
Map<? extends Serializable, List<Student>> collect1 = list.stream()
.collect(Collectors.groupingBy(a -> {
if (a.getGender() == null) {
return "null";
}
return a.getGender();
}));
//2根据性别分组后，再根据分数分组，>=60:A <60:B 为null的数据保留
Map<? extends Serializable, Map<String, List<Student>>> collect2 = list.stream().collect(Collectors.groupingBy(a -> {
if (a.getGender() == null) {
return "null";
}
return a.getGender();
}, Collectors.groupingBy(b -> {
String score = b.getScore();
if (score == null) {
return "B";
} else {
return score.compareTo("60") >= 0 ? "A" : "B";
}
})));
//3按照gender和height分组，TreeMap默认按key升序 TreeMap key不能为null
TreeMap<String, List<Student>> collect3 = list.stream().collect(Collectors.groupingBy(a -> {
if (a.getGender() == null || a.getHeight() == null) {
return "null";
}
return a.getGender() + "->" + a.getHeight();
}
, TreeMap::new
, Collectors.toList()));
//统计gender为1和0的人数
Map<? extends Serializable, Long> collect4 = list.stream()
.collect(Collectors.groupingBy(a -> {
if (a.getGender() == null) {
return "mix";
}
return a.getGender();
}
, counting()));
//按gender分组后，统计60为分界的人数
Map<String, Map<String, Long>> collect5 = list.stream().collect(
Collectors.groupingBy(//gender分组
a -> {
if (a.getGender() == null) {
return "null";//gender为null
}
return a.getGender() == 1 ? "M" : "F";
}
, Collectors.groupingBy(//60为分界
b -> {
String score = b.getScore();
if (score == null) {
return "null";
} else {
return score.compareTo("60") >= 0 ? "A" : "B";
}
}
, counting()//统计
)
));
//统计60分界的男女各多少
Map<String, Map<Integer, Long>> collect6 = list.stream()
.filter(a -> StringUtils.isNoneBlank(a.getScore()))//过滤score为""和null的数据
.filter(b -> b.getGender() != null)//过滤gender为null的数据
.collect(
Collectors.groupingBy(
c -> c.getScore().compareTo("60") >= 0 ? "G" : "B",//以60分组
Collectors.groupingBy(
Student::getGender,//以gender分组
counting()//统计
)
)
);
//统计男女各年龄之和
Map<Integer, Integer> collect7 = list.stream()
.filter(a -> a.getAge() != null || a.getGender() != null)
.collect(Collectors.groupingBy(Student::getGender,
Collectors.summingInt(Student::getAge)));
//分组元素存储在自定义集合
Map<Integer, TreeSet<Integer>> collect8 = list.stream()
.filter(a -> a.getGender() != null)
.collect(Collectors.groupingBy(Student::getGender,
Collectors.mapping(Student::getAge, toCollection(TreeSet::new))));
//计算男女中最高的分数
Map<Integer, Student> collect9 = list.stream().filter(a -> a.getGender() != null)
.collect(Collectors.groupingBy(
Student::getGender, Collectors.collectingAndThen(Collectors.maxBy(Comparator.comparing(Student::getScore)), Optional::get)
)
);
//计算男女中最低的分数
Map<Integer, Student> collect10 = list.stream().filter(a -> a.getGender() != null)
.collect(Collectors.toMap(Student::getGender, Function.identity(), BinaryOperator.minBy(Comparator.comparing(Student::getScore)))
);
// //计算男女中最高的分数 分数相同去用时最短
Map<Integer, Student> collect11 = list.stream().filter(a -> a.getGender() != null)
.collect(Collectors.toMap(
Student::getGender,//性别
Function.identity(),//t->t
BinaryOperator.maxBy(
Comparator.comparing(Student::getScore)//分数比较
.thenComparing(b -> b.getEndTime().getTime() - b.getStartTime().getTime()//分数相同，按时间比较
, Comparator.reverseOrder()))//外层用的max，故此处排序取反
)
);
//相同的存放在list中
TreeMap<Integer, Student> collect12 = list.stream().filter(a -> a.getGender() != null)
.collect(Collectors.toMap(
Student::getGender,
Function.identity(),
BinaryOperator.maxBy(
Comparator.comparing(Student::getScore)
.thenComparing(b -> b.getEndTime().getTime() - b.getStartTime().getTime()
, Comparator.reverseOrder())
),
TreeMap::new
)
);
HashMap<Integer, List<Student>> hashMap = new HashMap<>();
collect12.forEach((k, v) -> {
Map<Integer, ArrayList<Student>> listMap = list.stream()
.filter(a ->
k.equals(a.getGender())
&& v.getScore().equals(a.getScore())
&& (a.getEndTime().getTime()-a.getStartTime().getTime())==(v.getEndTime().getTime() - v.getStartTime().getTime())
)
.collect(Collectors.toMap(
Student::getGender,
t -> {
List<Student> students = Collections.singletonList(t);
return new ArrayList<>(students);
},
(v1, v2) -> {
v2.addAll(v1);
return v2;
})
);
hashMap.putAll(listMap);
});
//分数最高用时最短
Optional<Student> max = list.stream().max(Comparator
.comparing(Student::getScore)
.thenComparing(a -> a.getEndTime().getTime() - a.getStartTime().getTime(),
Comparator.reverseOrder())
);
Student student = max.isPresent() ? max.get() : null;
//最大值 分数 用时
Student student1 = list.stream().max(Comparator
.comparing(Student::getScore)
.thenComparing(a -> a.getEndTime().getTime() - a.getStartTime().getTime(),
Comparator.reverseOrder())
).orElse(null);
//男女各组的平均分数
Map<Integer, Double> collect13 = list.stream()
.filter(a -> a.getGender() != null)
.filter(b -> StringUtils.isNoneBlank(b.getScore()))
.collect(Collectors.groupingBy(Student::getGender,
Collectors.averagingDouble(a -> Double.parseDouble(a.getScore()))));
System.out.println();
}
} |
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