java - 将 Java List 转换为 Pivot 格式

Question

我有一个下面的类，想用 java 将数据对象列表转换为数据透视表格式。

public class Data {

    private String consultedOn;
    private String consultedBy;

    // Getters

    // Setters


}


List<Data> reports = new ArrayList<Data>();

reports.add(new Data("04/12/2018","Mr.Bob"));
reports.add(new Data("04/12/2018","Mr.Jhon"));
reports.add(new Data("04/12/2018","Mr.Bob"));
reports.add(new Data("05/12/2018","Mr.Jhon"));
reports.add(new Data("06/12/2018","Mr.Bob"));
reports.add(new Data("06/12/2018","Mr.Jhon"));
reports.add(new Data("07/12/2018","Mr.Bob"));

我想在集合中用 java 将上面的列表转换成下面的表格格式。

consultedOn       Mr.Bob          Mr.Jhon  
---------------------------------------
04/12/2018           2              1
05/12/2018           0              1
06/12/2018           1              1
07/12/2018           1              0

请注意，consultedOn 字段不限于两个值，该字段可以包含任何数据，因此集合应该是动态的。

我尝试通过以下代码使用 Java8 流。

class DataMap {


 private String consultedOn;
    private String consultedBy;

    public DataMap(String consultedOn) {
        super();
        this.consultedOn = consultedOn;
    }

    public DataMap(String consultedOn, String consultedBy) {
        super();
        this.consultedOn = consultedOn;
        this.consultedBy = consultedBy;
    }


    public String getConsultedOn() {
        return consultedOn;
    }


    public void setConsultedOn(String consultedOn) {
        this.consultedOn = consultedOn;
    }


    public String getConsultedBy() {
        return consultedBy;
    }


    public void setConsultedBy(String consultedBy) {
        this.consultedBy = consultedBy;
    }


    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((consultedOn == null) ? 0 : consultedOn.hashCode());
        return result;
    }


    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (!(obj instanceof DataMap ))
            return false;
        DataMap other = (DataMap )obj;
        if (consultedOn == null) {
            if (other.consultedOn != null)
                return false;
        } else if (!consultedOn.equals(other.consultedOn))
            return false;
        return true;
    }


}


Map<DataMap, List<DataReport>> map = reports.stream()
            .collect(Collectors.groupingBy(x -> new DataMap(x.getConsultedOn(), x.getConsultedBy())));

但是 map 并没有按照我的预期给出预期的结果。

我不确定如何继续处理此类数据，我们将不胜感激。

Answer 1

这是一个完整的答案，使用我在评论中解释的技术，即设计一个类 Row 代表您要为每一行生成的内容，即 consultedOn 字符串，以及每个人的咨询次数。

public class Pivot {
    private static final class Data {

        private final String consultedOn;
        private final String consultedBy;

        public Data(String consultedOn, String consultedBy) {
            this.consultedOn = consultedOn;
            this.consultedBy = consultedBy;
        }

        public String getConsultedOn() {
            return consultedOn;
        }

        public String getConsultedBy() {
            return consultedBy;
        }
    }

    private static final class Row {
        private final String consultedOn;
        private final Map<String, Integer> consultationsByPerson = new HashMap<>();

        public Row(String consultedOn) {
            this.consultedOn = consultedOn;
        }

        public void addPerson(String person) {
            consultationsByPerson.merge(person, 1, Integer::sum);
        }

        public int getConsultationsFor(String person) {
            return consultationsByPerson.getOrDefault(person, 0);
        }

        public String getConsultedOn() {
            return consultedOn;
        }
    }

    private static class PivotReport {

        private final Map<String, Row> rowsByConsultedOn = new HashMap<>();
        private SortedSet<String> persons = new TreeSet<>();

        private PivotReport() {}

        private void addData(Data d) {
            rowsByConsultedOn.computeIfAbsent(d.getConsultedOn(), Row::new).addPerson(d.getConsultedBy());
            persons.add(d.consultedBy);
        }

        public static PivotReport create(List<Data> list) {
            PivotReport report = new PivotReport();
            list.forEach(report::addData);
            return report;
        }

        public String toString() {
            String headers = "Consulted on\t" + String.join("\t", persons);
            String rows =  rowsByConsultedOn.values()
                                            .stream()
                                            .sorted(Comparator.comparing(Row::getConsultedOn))
                                            .map(this::rowToString)
                                            .collect(Collectors.joining("\n"));
            return headers + "\n" + rows;
        }

        private String rowToString(Row row) {
            return row.getConsultedOn() + "\t" +
                persons.stream()
                       .map(person -> Integer.toString(row.getConsultationsFor(person)))
                       .collect(Collectors.joining("\t"));
        }
    }


    public static void main(String[] args) {
        List<Data> list = createListOfData();
        PivotReport report = PivotReport.create(list);
        System.out.println(report);
    }

    private static List<Data> createListOfData() {
        List<Data> reports = new ArrayList<Data>();

        reports.add(new Data("04/12/2018","Mr.Bob"));
        reports.add(new Data("04/12/2018","Mr.Jhon"));
        reports.add(new Data("04/12/2018","Mr.Bob"));
        reports.add(new Data("05/12/2018","Mr.Jhon"));
        reports.add(new Data("06/12/2018","Mr.Bob"));
        reports.add(new Data("06/12/2018","Mr.Jhon"));
        reports.add(new Data("07/12/2018","Mr.Bob"));
        reports.add(new Data("07/12/2018","Mr.Smith"));

        return reports;
    }
}

请注意，由于您对 consultedOn 字段使用的是 String 而不是 LocalDate，因此日期将按字典顺序排序，而不是按时间顺序排序。您应该使用适当的类型:LocalDate。