在Java8中收集统计数据
我想在对一组数据进行分组后收集统计数据,但我不知道这是否可行在Java8中收集统计数据,java,lambda,java-8,functional-programming,java-stream,Java,Lambda,Java 8,Functional Programming,Java Stream,我想在对一组数据进行分组后收集统计数据,但我不知道这是否可行 Map<String, DoubleSummaryStatistics> menuStatistics = menuPrices.parallelStream() .collect(Collectors.groupingBy(cp -> dt1.format(cp.getUpdateDate())),
Map<String, DoubleSummaryStatistics> menuStatistics =
menuPrices.parallelStream()
.collect(Collectors.groupingBy(cp -> dt1.format(cp.getUpdateDate())),
Collector.of(DoubleSummaryStatistics::new));
地图菜单统计=
menuPrices.parallelStream()
.collect(Collectors.groupingBy(cp->dt1.format(cp.getUpdateDate()),
Collector.of(DoubleSummaryStatistics::new));
因为我有一些编译问题:
Multiple markers at this line
- The method of(Supplier<R>, BiConsumer<R,T>, BinaryOperator<R>, Collector.Characteristics...) in the type Collector is not applicable for the arguments
(DoubleSummaryStatistics::new)
- The constructed object of type DoubleSummaryStatistics is incompatible with the descriptor's return type: R
此行有多个标记
-类型收集器中的方法(Supplier、BiConsumer、BinaryOperator、Collector.Characteristics…)不适用于参数
(DoubleSummaryStatistics::新建)
-构造的DoubleSummaryStatistics类型的对象与描述符的返回类型不兼容:R
您需要使用收集器。SummaringDouble()
,假设您的类(流的元素类型)有一些double
属性,您要为其计算统计信息:
Map<String, DoubleSummaryStatistics>
menuStatistics =
menuPrices.parallelStream()
.collect(Collectors.groupingBy(cp -> dt1.format(cp.getUpdateDate()),
Collectors.summarizingDouble(cp -> cp.getSomeDoubleValue())));
Map
菜单统计=
menuPrices.parallelStream()
.collect(Collectors.groupingBy(cp->dt1.format(cp.getUpdateDate()),
Collectors.summaringdouble(cp->cp.getSomeDoubleValue());
试试这个menuPrices.parallelStream().collect(Collectors.groupingBy(cp->dt1.format(cp.getUpdateDate()),Collectors.summaringDouble(YourClass::someProperty))代码>