根据 Map 输入从 Collection<Objects> 中提取对象

Question

我收集了大约 13360 个帐户对象，如下所示

输入数据：

Account(id,date,balance,region,cost)
Account("1","2019-07-24","X,"Y","Z")
Account("1","2019-07-24","C,"Y","Z")
Account("1","2019-07-23","X,"D","Z")
Account("1","2019-07-23","X,"Y","f")
Account("1","2019-07-22","X,"s","Z")

Account("2","2019-07-23","X,"A","Z")
Account("2","2019-07-23","X,"Y","d")
Account("2","2019-07-22","d,"Y","Z")
Account("2","2019-07-23","X,"s","Z")

Account("3","2019-07-24","d,"Y","d")

Account("4","2019-07-24","X,"Y","Z")
Account("4","2019-07-23","d,"Y","Z")

Account("5","2019-07-23","X,"d","Z")
Account("5","2019-07-22","X,"Y","Z")

过滤条件：

Map<id,date>
(1,2019-07-24), (2,2019-07-23),(5,2019-07-23)

预期结果是

Account("1","2019-07-24","X,"Y","Z")
Account("1","2019-07-24","C,"Y","Z")

Account("2","2019-07-23","X,"A","Z")
Account("2","2019-07-23","X,"Y","d")
Account("2","2019-07-23","X,"s","Z")

Account("5","2019-07-23","X,"d","Z")

因此我想检索某些帐户的最新数据

下面的代码示例只为我提供最近日期的数据，即特定帐户列表的（今天的日期）。但对于某些帐户，我没有今天日期的数据，因此我需要检索可用的最新数据

EntryObject eo = new PredicateBuilder.getEntryObject();
Predicate p = eo.get("id").in(1,2,5).and(eo.get("date").equals(todaysdate))
Collection<Account> coll = accounts.values(p);

Answer 1

您可以在 filteras:

中使用 anyMatch

List<Account> filteredAccounts = acccounts.stream()
        .filter(acc -> map.entrySet()
                .stream()
                .anyMatch(e -> e.getKey().equals(acc.getId())
                        && e.getValue().equals(acc.getDate())))
        .collect(Collectors.toList());

Answer 2

这是一个更通用的解决方案，只获取一组 accountIds 的最新条目：

Set<Integer> accountIds = Set.of(1, 2, 5);
List<Account> result = accounts.stream()
        .filter(a -> accountIds.contains(a.getId()))
        .collect(Collectors.groupingBy(Account::getId, Collectors.groupingBy(Account::getDate, TreeMap::new, Collectors.toList())))
        .values().stream()
        .flatMap(m -> m.lastEntry().getValue().stream())
        .collect(Collectors.toList());

首先，您仅根据 ID 过滤所需的帐户。之后你按 id 和日期对它们进行分组，这会给你这个中间结果：

{
  1: {
    2019-07-22: [{id: 1, date: 2019-07-22, balance: 'X', region: 's', cost: 'Z'}], 
    2019-07-23: [{id: 1, date: 2019-07-23, balance: 'X', region: 'D', cost: 'Z'}, {id: 1, date: 2019-07-23, balance: 'X', region: 'Y', cost: 'f'}],
    2019-07-24: [{id: 1, date: 2019-07-24, balance: 'X', region: 'Y', cost: 'Z'}, {id: 1, date: 2019-07-24, balance: 'C', region: 'Y', cost: 'Z'}]
  }, 
  2: {
    2019-07-22: [{id: 2, date: 2019-07-22, balance: 'd', region: 'Y', cost: 'Z'}], 
    2019-07-23: [{id: 2, date: 2019-07-23, balance: 'X', region: 'A', cost: 'Z'}, {id: 2, date: 2019-07-23, balance: 'X', region: 'Y', cost: 'd'}, {id: 2, date: 2019-07-23, balance: 'X', region: 's', cost: 'Z'}]
  }, 
  5: {
    2019-07-22: [{id: 5, date: 2019-07-22, balance: 'X', region: 'Y', cost: 'Z'}], 
    2019-07-23: [{id: 5, date: 2019-07-23, balance: 'X', region: 'd', cost: 'Z'}]
  }
}

最后，您只使用生成的地图的值，flatMap 它与分组 TreeMap 的最后一个值一起使用，以仅获取具有最新日期的列表。

最终结果是这样的：

[
  {id: 1, date: 2019-07-24, balance: 'X', region: 'Y', cost: 'Z'}, 
  {id: 1, date: 2019-07-24, balance: 'C', region: 'Y', cost: 'Z'}, 

  {id: 2, date: 2019-07-23, balance: 'X', region: 'A', cost: 'Z'}, 
  {id: 2, date: 2019-07-23, balance: 'X', region: 'Y', cost: 'd'}, 
  {id: 2, date: 2019-07-23, balance: 'X', region: 's', cost: 'Z'},

  {id: 5, date: 2019-07-23, balance: 'X', region: 'd', cost: 'Z'}
]

根据 Map 输入从 Collection<Objects> 中提取对象

Extract Objects from Collection<Objects> based on a Map input

java

java-stream

predicate

predicatebuilder