根据条件在列表中间添加一个对象

Question

我有一个如下所示的排序列表

我用下面的代码排序了。

             Comparator<MyBean> typeComparator = Comparator.comparing(MyBean::getType);

             Comparator<MyBean> costComparator = Comparator.comparing(MyBean::getCost);

             Comparator<MyBean> multipleFieldsComparator = typeComparator.thenComparing(costComparator); 
             
             Collections.sort(mbList, multipleFieldsComparator);

现在我用下面的代码确定每个 Type 的总成本。

Map<String, Double> sum = mbList.stream().collect(
                        Collectors.groupingBy(MyBean::getType, Collectors.summingDouble(MyBean::getCost)));

这里我有每种类型的总成本。像 A = 109490.03 和 B = 4431.218

现在我需要在 mbList 列表的中间添加这个 Total Cost 对象。

我想要的输出应该如下所示

我的整个代码如下。

             Comparator<MyBean> typeComparator = Comparator.comparing(MyBean::getType);

             Comparator<MyBean> costComparator = Comparator.comparing(MyBean::getCost);

             Comparator<MyBean> multipleFieldsComparator = typeComparator.thenComparing(costComparator); 
             
             Collections.sort(mbList, multipleFieldsComparator);
             
             
             Map<String, Double> sum = mbList.stream().collect(
                        Collectors.groupingBy(MyBean::getType, Collectors.summingDouble(MyBean::getCost)));
            System.out.println(" $$$$$$$$$$$$$$$$$ "+sum);
            
            for (MyBean mb : mbList) {

                row = sheetType.createRow(sheetType.getPhysicalNumberOfRows());
                cell = row.createCell(cellnum++);
                cell.setCellValue((String) mb.getType() + "-" + mb.getCategory());
                cell = row.createCell(cellnum++);
                cell.setCellValue(mb.getCost());
                cellnum = 0;
            }

MyBean.java

public class MyBean{
    private String type;
    private Double total;
    private String xxx;
    private String yyy;

    //setters and getters
}

我的问题是如何在每个排序值的末尾添加 Total cost，例如在 A 之后需要添加总成本，在 B 之后我们可以添加总计成本....

Answer 1

这里是想法的快速草稿，肯定有比这更好的解决方案，但这可以解决问题（稍后将更新此答案以改进代码）

lastMatch = "", totalCost = 0;
for ( mbList i = 0 -> n) {
    currentMatch = mbList[i].getType(); // return A- or B- ...
    if(currentMatch != lastMatch){
        if(lastMatch != ""){
            > print totalCost; // to avoid printing Total cost at first row
        }
        lastMatch = currentMatch;
        totalCost = 0;
    }
    > print col name = col value
    totalCost += mbList[i].getCost(); // keep adding cost for your currentRegExrMatch
}

Answer 2

你就快完成了，但不是直接汇总总和，而是先按类型分组，然后计算每个子列表的总和：

a) 按类型分组

Map<String, List<MyBean>> byType = mbList.stream()
                                         .sorted(multipleFieldsComparator)
                                         .collect(
                                             Collectors.groupingBy(
                                                 MyBean::getType,
                                                 LinkedHashMap::new, // preserves order
                                                 Collectors.toList()
                                             ));

b) 计算每种类型的总和

for (Entry<String, List<MyBean>> entry : byType.entrySet()) {
    List<MyBean> typeList = entry.getValue();
    double sum = typeList.stream().mapToDouble(MyBean::getCost).sum();
    typeList.add(new MyBean(entry.getKey(), sum));
}

c) 将所有列表展平为一个大列表（它们已经正确排序）

List<MyBean> listWithSums = byType.values()
                                  .stream()
                                  .flatMap(List::stream)
                                  .collect(Collectors.toList());

根据条件在列表中间添加一个对象

add an object in middle of the list based on the condition

java

collections

arraylist