Java实现多字段分组计数

比眉伴天荒 2021-07-24 20:04 533阅读 0赞

# 一 需求 #

以产品类型和国家两个字段为关键字，进行计数。比如中国的电脑有多少种，韩国的洗衣机有多少种？

# 二 代码 #

package com.cakin.javademo;
 
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.stream.Collectors;
 
 /**
 * @ClassName: GroupCount
 * @Description: 分组计数 参考：http://www.cielni.com/2018/07/14/java-stream-groupingby/
 * @Date: 2021/3/13
 * @Author: cakin
 */
 public class GroupCount {
 /**
 * 功能描述：分组计数
 *
 * @author cakin
 * @date 2021/3/14
 * @param args 命令行
 * @description: 以 产品类型 和 国家 多字段为关键字，进行计数
 */
 public static void main(String[] args) {
 List<Record> records = new ArrayList<>();
 records.add(new Record("电脑", "中国", "台式"));
 records.add(new Record("洗衣机", "韩国", "滚筒"));
 records.add(new Record("电脑", "中国", "笔记本"));
 records.add(new Record("洗衣机", "韩国", "一般"));
 records.add(new Record("电脑", "中国", "平板"));
 records.add(new Record("洗衣机", "中国", "笔记本"));
 records.add(new Record("电脑", "韩国", "滚筒"));
 records.add(new Record("电脑", "韩国", "平板"));
 records.add(new Record("洗衣机", "中国", "一般"));
 
 // 以 productType 和 country 两个字段为关键字，进行计数（Collectors.counting()）
 Map<String, Long> countMap = records
 .stream()
 .collect(Collectors.groupingBy(o -> o.getProductType() + "_" + o.getCountry(), Collectors.counting()));
 
 List<Record> countRecords = countMap.keySet().stream().map(key -> {
 String[] temp = key.split("_");
 String productType = temp[0];
 String country = temp[1];
 Record record = new Record();
 record.setProductType(productType);
 record.setCountry(country);
 record.setCount(countMap.get(key).intValue());
 return record;
 }).collect(Collectors.toList());
 for (Record countRecord : countRecords) {
 System.out.println(countRecord);
 }
 }
 }
 
 class Record {
 /**
 * 产品类型
 */
 private String productType;
 /**
 * 国家
 */
 private String Country;
 /**
 * 风格
 */
 private String style;
 /**
 * 计数
 */
 private int count;
 
 public String getProductType() {
 return productType;
 }
 
 public void setProductType(String productType) {
 this.productType = productType;
 }
 
 public String getCountry() {
 return Country;
 }
 
 public void setCountry(String country) {
 Country = country;
 }
 
 public Record() {
 }
 
 public Record(String productType, String country, String style) {
 this.style = style;
 this.productType = productType;
 this.Country = country;
 }
 
 
 public String getStyle() {
 return style;
 }
 
 public void setStyle(String style) {
 this.style = style;
 }
 
 public int getCount() {
 return count;
 }
 
 public void setCount(int count) {
 this.count = count;
 }
 
 @Override
 public String toString() {
 return "Record{" +
 "productType='" + productType + '\'' +
 ", Country='" + Country + '\'' +
 ", count=" + count +
 '}';
 }
 }

# 三 测试 #

Record{productType='洗衣机', Country='中国', count=2}
    Record{productType='电脑', Country='中国', count=3}
    Record{productType='洗衣机', Country='韩国', count=2}
    Record{productType='电脑', Country='韩国', count=2}