如何計算基於Java 8 Stream過濾器輸出的百分比

Question

我想獲取作業列表（稱爲resultStream）並計算完全完成的作業百分比。

public class Job { 
    private Date date; 
    private String success; 

    // Getter and setter and constructor. 
} 

列表包含以下內容：

new Job("TODAY", "YES"); 
new Job("TODAY", "YES"); 
new Job("YESTERDAY", "YES"); 
new Job("TODAY", "NO"); 

這裏是我的代碼至今：

resultStream.stream().parallel().filter(result -> { 
    if ("YES".contains(result.getSuccess())) { 
     return true;   
    } else { 
     return false; 
    } 
}).collect(groupingBy(Job::getDate, HashMap::new, counting())); 

這將返回我一個HashMap（日期，龍）具有以下內容：
今天，2
昨天1

其實我是想了以下結果：
今天，66％
YESTERDAY，100％

在此先感謝。

Answer 1

平均爲雙可以爲這樣做：

public static void main(final String... args) { 
    final List<Job> jobs = new ArrayList<>(); 
    jobs.add(new Job(LocalDate.now(), "YES")); 
    jobs.add(new Job(LocalDate.now(), "NO")); 
    jobs.add(new Job(LocalDate.now(), "YES")); 
    jobs.add(new Job(LocalDate.now() 
      .minusDays(1), "YES")); 

    final Map<LocalDate, Double> result = jobs.stream() 
     .collect(
        Collectors.groupingBy(Job::getDate, 
          Collectors.mapping(Job::getSuccess, Collectors.averagingDouble(success -> { 
           return "YES".equals(success) ? 1 : 0; 
          })))); 

    // result = {2014-07-20=1.0, 2014-07-21=0.6666666666666666} 
    System.out.println(result); 
} 

作爲字符串：

public static void main(final String... args) { 
    final List<Job> jobs = new ArrayList<>(); 
    jobs.add(new Job(LocalDate.now(), "YES")); 
    jobs.add(new Job(LocalDate.now(), "NO")); 
    jobs.add(new Job(LocalDate.now(), "YES")); 
    jobs.add(new Job(LocalDate.now() 
      .minusDays(1), "YES")); 

    final Map<LocalDate, String> result = jobs.stream() 
      .collect(
        Collectors.groupingBy(
          Job::getDate, 
          Collectors.collectingAndThen(
            Collectors.mapping(Job::getSuccess, Collectors.averagingDouble(success -> { 
             return "YES".equals(success) ? 1 : 0; 
            })), avg -> String.format("%,.0f%%", avg * 100)))); 
    // result = {2014-07-20=100%, 2014-07-21=67%} 
    System.out.println(result); 
}