List stream 对象 属性去重
2023-09-14 08:59:54 时间
单值去重不写了,记录对象去重
随手一个对象:
@Data @AllArgsConstructor public class Milk { private Integer key; private String value; }
操作:
package com.yus.util; import java.util.*; import java.util.stream.Collectors; import static java.util.Comparator.comparing; import static java.util.Comparator.comparingLong; import static java.util.stream.Collectors.collectingAndThen; import static java.util.stream.Collectors.toCollection; public class main { public static void main(String[] args) { Milk milk0=new Milk(0,"a"); Milk milk1=new Milk(1,"b"); Milk milk2=new Milk(0,"c"); List<Milk> list=new ArrayList<>(); list.add(milk0); list.add(milk1); list.add(milk2); //去重 List<Milk> uniqueMilk = list.stream().collect( collectingAndThen( toCollection(() -> new TreeSet<>(comparing(n->n.getKey()))),ArrayList::new) ); for (Milk m:uniqueMilk) { System.out.println(m.toString()); } } }
操作底层是set,视图,collection...一堆东西,还是有点意思的,不记录了,有兴趣可深入
任何Object类型去重...~
import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; import java.util.function.Function; import java.util.function.Predicate; import java.util.stream.Collectors; public class TestMain { public static void main(String[] args) { List<Map<String, Object>> list = new ArrayList<>(); Map<String, Object> map = new HashMap<>(); map.put("id", "11"); map.put("orderno", "No.1"); list.add(map); Map<String, Object> map1 = new HashMap<>(); map1.put("id", "2222"); map1.put("orderno", "No.2"); list.add(map1); Map<String, Object> map2 = new HashMap<>(); map2.put("id", "33"); map2.put("orderno", "No.2"); list.add(map2); Map<String, Object> map3 = new HashMap<>(); map3.put("id", "444"); map3.put("orderno", "No.1"); list.add(map3); List<Map<String, Object>> collect = list.stream().filter(distinctByKey(n -> n.get("orderno"))) .collect(Collectors.toList()); collect.forEach(System.out::println); } private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) { ConcurrentHashMap<Object, Boolean> map = new ConcurrentHashMap<>(); return t -> map.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null; } }
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