非常に包括的なlambda式はリストセットを再削除し、グループ化し、ソートし、フィルタリングし、和を求め、最値メソッドツールクラス
97495 ワード
私たちはよくリストの集合を重くします.そこで、私は自分で時間をかけてlambda式でリストの集合をどのようにカプセル化してテストして、後で迅速に使用することができます.オブジェクトのセット内の属性の重み付けなどが含まれます.特殊なリストの再削除要求があれば、以下の方法を自分で修正することができます.
以下の方法は本人が比較的簡単な書き方を検証したので、参考にしてください.
文書ディレクトリ一、重量除去 二、並べ替え 三、濾過、加算、最値 一、重さを取り除く
二、並べ替え
三、濾過、求和、最値
以下の方法は本人が比較的簡単な書き方を検証したので、参考にしてください.
文書ディレクトリ
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;
public class ListUtil {
public static List<String> list = Arrays.asList("1","2","2","3","3","4","4","5","6","7","8");
public static List<City> cities = null;
static {
cities = new ArrayList<City>(){
{
add(new City(" ",11));
add(new City(" ",22));
add(new City(" ",55));
add(new City(" ",33));
add(new City(" ",33));
add(new City(" ",43));
}
};
}
public static void main(String[] args) {
System.out.println(ListUtil.distinctElements(list));
System.out.println(ListUtil.getNoDuplicateElements(list));
System.out.println(ListUtil.getDuplicateElements(list));
System.out.println(ListUtil.getDuplicateElementsForObject(cities));
System.out.println(ListUtil.getNoDuplicateElementsForObject(cities));
System.out.println(ListUtil.getElementsAfterDuplicate(cities));
System.out.println(ListUtil.getDuplicateObject(cities));
System.out.println(ListUtil.getNoDuplicateObject(cities));
System.out.println(ListUtil.distinctObject(cities));
}
// [1, 2, 3, 4, 5, 6, 7, 8]
public static <T> List<T> distinctElements(List<T> list) {
return list.stream().distinct().collect(Collectors.toList());
}
//lambda [1, 5, 6, 7, 8]
public static <T> List<T> getNoDuplicateElements(List<T> list) {
// Map， ，
Map<T, Long> map = list.stream().collect(Collectors.groupingBy(p -> p,Collectors.counting()));
System.out.println("getDuplicateElements2: "+map);
return map.entrySet().stream() // Set Stream
.filter(entry -> entry.getValue() == 1) // 1 entry
.map(entry -> entry.getKey()) // entry （ ） Stream
.collect(Collectors.toList()); // List
}
//lambda [2, 3, 4]
public static <T> List<T> getDuplicateElements(List<T> list) {
return list.stream().collect(Collectors.collectingAndThen(Collectors
.groupingBy(p -> p, Collectors.counting()), map->{
map.values().removeIf(size -> size ==1); // >1 ；== 1
List<T> tempList = new ArrayList<>(map.keySet());
return tempList;
}));
}
// set
public static <T> Set<T> getDuplicateElements2(List<T> list) {
Set<T> set = new HashSet<>();
Set<T> exist = new HashSet<>();
for (T s : list) {
if (set.contains(s)) {
exist.add(s);
} else {
set.add(s);
}
}
return exist;
}
/**----------- List --------------*/
// [ , ]
public static List<String> getDuplicateElementsForObject(List<City> list) {
return list.stream().collect(Collectors.groupingBy(p -> p.getCity(),Collectors.counting())).entrySet().stream()
.filter(entry -> entry.getValue() > 1) // >1 ；==
.map(entry -> entry.getKey())
.collect(Collectors.toList());
}
// [ , ]
public static List<String> getNoDuplicateElementsForObject(List<City> list){
Map<String,List<City>> map = list.stream().collect(Collectors.groupingBy(City::getCity));
return map.entrySet().stream().filter(entry -> entry.getValue().size() == 1)
.map(entry -> entry.getKey()) // entry （ ） Stream
.collect(Collectors.toList()); // List
}
// [ , , , ]
public static List<String> getElementsAfterDuplicate(List<City> list) {
return list.stream().map(o->o.getCity()).distinct().collect(Collectors.toList());
}
//
// [[City(city= , total=11), City(city= , total=33)], [City(city= , total=22), City(city= , total=55)]]
public static List<List<City>> getDuplicateObject(List<City> list) {
return list.stream().collect(Collectors.groupingBy(City::getCity)).entrySet().stream()
.filter(entry -> entry.getValue().size() > 1) // >1 ；==
.map(entry -> entry.getValue())
.collect(Collectors.toList());
}
//
//[[City(city= , total=43)], [City(city= , total=33)]]
public static List<City> getNoDuplicateObject(List<City> list) {
List<City> cities = new ArrayList<>();
list.stream().collect(Collectors.groupingBy(City::getCity)).entrySet().stream()
.filter(entry -> entry.getValue().size() ==1) //>1 ；== ;
.map(entry -> entry.getValue())
.forEach(p -> cities.addAll(p));
return cities;
}
//
//[City(city= , total=11), City(city= , total=22), City(city= , total=33), City(city= , total=43)]
public static List<City> distinctObject(List<City> list) {
return list.stream().filter(distinctByKey(City::getCity)).collect(Collectors.toList());
}
public static <T> Predicate<T> distinctByKey(Function<? super T, Object> keyExtractor) {
Map<Object, Boolean> seen = new ConcurrentHashMap<>();
return object -> seen.putIfAbsent(keyExtractor.apply(object), Boolean.TRUE) == null;
}
}
二、並べ替え
import java.util.*;
import java.util.stream.Collectors;
public class ListUtil_sort {
public static List<Integer> list = Arrays.asList(10,1,6,4,8,7,9,3,2,5);
public static List<City> cities = null;
public static List<City> cities2 = null;
static {
cities = new ArrayList<City>(){
{
add(new City(" ",11));
add(new City(" ",55));
add(new City(" ",33));
add(new City(" ",33));
}
};
cities2 = new ArrayList<City>(){
{
add(new City(" ",11,11));
add(new City(" ",55,22));
add(new City(" ",33,55));
add(new City(" ",33,44));
}
};
}
public static void main(String[] args) {
System.out.println(sort(list));
System.out.println(reversed(list));
System.out.println(sortForObject(cities));
System.out.println(reversedForObject(cities));
System.out.println(sortForObject2(cities2));
}
//list
public static <T> List<T> sort(List<T> list){
return list.stream().sorted().collect(Collectors.toList());
}
//list
public static List<Integer> reversed(List<Integer> list){
return list.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());
}
//
public static List<City> sortForObject(List<City> list){
return list.stream().sorted(Comparator.comparing(City::getTotal)).collect(Collectors.toList());
}
//
public static List<City> reversedForObject(List<City> list){
return list.stream().sorted(Comparator.comparing(City::getTotal).reversed()).collect(Collectors.toList());
}
//
public static List<City> sortForObject2(List<City> list){
return list.stream().sorted(Comparator.comparing(City::getTotal).thenComparing(City::getNum)).collect(Collectors.toList());
}
}
三、濾過、求和、最値
import java.util.*;
import java.util.stream.Collectors;
public class ListUtil_sum {
public static List<Integer> list = Arrays.asList(10,1,6,4,8,7,9,3,2,5);
public static List<String> strList = Arrays.asList("10","1","6","4");
public static List<City> cities = null;
public static Map<String,Integer> cityMap = null;
static {
cities = new ArrayList<City>(){
{
add(new City(" ",11));
add(new City(" ",55));
add(new City(" ",45));
add(new City(" ",33));
}
};
cityMap = new HashMap<>();
cityMap.put(" ",55);
cityMap.put(" ",11);
}
public static void main(String[] args) {
System.out.println(calculation(list));
calculation2(cities);
listToMap(cities);
mapToList(cityMap);
stringToList(" 、 ");
joinStringValueByList(cities);
joinStringValueByList2(strList);
System.out.println(filter(cities));
}
//
///IntSummaryStatistics{count=4, sum=132, min=11, average=33.000000, max=55}
public static IntSummaryStatistics calculation(List<Integer> list){
IntSummaryStatistics stat = list.stream().collect(Collectors.summarizingInt(p -> p));
System.out.println("max:"+stat.getMax());
System.out.println("min:"+stat.getMin());
System.out.println("sum:"+stat.getSum());
System.out.println("count:"+stat.getCount());
System.out.println("average:"+stat.getAverage());
return stat;
}
//
public static void calculation2(List<City> list){
System.out.println("sum="+ list.stream().mapToInt(City::getTotal).sum());
System.out.println("max="+ list.stream().mapToInt(City::getTotal).max().getAsInt());
System.out.println("min="+ list.stream().mapToInt(City::getTotal).min().getAsInt());
System.out.println("ave="+ list.stream().mapToInt(City::getTotal).average().getAsDouble());
}
// List map
public static void listToMap(List<City> list){
// (k1,k2)->k1 ， key, key1, key2
Map<String,City> map = list.stream().collect(Collectors.toMap(City::getCity,city -> city, (k1, k2) -> k1));
map.forEach((k,v) -> System.out.println("k=" + k + ",v=" + v));
}
//
public static void calculation11(List<City> list){
Map<String, IntSummaryStatistics> intSummaryStatistics = list.stream().
collect(Collectors.groupingBy(i -> i.getCity(), Collectors.summarizingInt(City::getTotal)));
System.out.println("-4-->" + intSummaryStatistics);
System.out.println("-5-->" + intSummaryStatistics.get(" ").getSum());
}
// map list
public static void mapToList(Map<String,Integer> map){
List<City> list = map.entrySet().stream().map(key -> new City(key.getKey(),key.getValue())).collect(Collectors.toList());
System.out.println(list);
list.forEach(bean -> System.out.println(bean.getCity() + "," + bean.getTotal()));
}
// list
public static void stringToList(String str){
//
// list = Arrays.asList(str.split(","));
//
List<String> list = Arrays.asList(str.split(",")).stream().map(string -> String.valueOf(string)).collect(Collectors.toList());
list.forEach(string -> System.out.println(string));
}
//
public static void joinStringValueByList(List<City> list){
System.out.println(list.stream().map(City::getCity).collect(Collectors.joining(",")));
}
//
public static void joinStringValueByList2(List<String> list){
//
System.out.println(String.join(",", list));
//
System.out.println(list.stream().collect(Collectors.joining(",")));
}
//
public static List<City> filter(List<City> list){
return list.stream().filter(a -> a.getTotal()>44).collect(Collectors.toList());
}
}