Java - Lambda筛选条件,忽略添加到地图 [英] Java - Lambda filter criteria, to ignore adding to map
问题描述
我有格式的地图(参考使用Lambda查找平均值(双字符串存储))
地图< String,Double> ():
.filter(objectDTO - >!objectDTO.getNewIndex()。isEmpty())
。 collect(Collectors.groupingBy(ObjectDTO :: getCountryName,
Collectors.mapping(ObjectDTO :: getNewIndex,
Collectors.averagingDouble(Double :: parseDouble))));
我想忽略忽略整个国家/地区的映射,即使其中一个是newIndex值country is empty?
由于 Collectors.groupingBy
不允许跳过组,您必须提前分析过滤条件,以便您可以在执行 groupBy
之前进行过滤,或者之后过滤映射(我忽略第三个选项,实现您自己的 groupingBy
收藏家。
-
提前分析:
Map< String,Boolean> hasEmpty = mapOfIndicators.values()。stream()
.flatMap(Collection :: stream)
.collect(Collectors.groupingBy(ObjectDTO :: getCountryName,
)Collectors.mapping(o-> o.getNewIndex()。isEmpty(),
Collectors.reducing(false,Boolean :: logicalOr)) ));
Map< String,Double> averages = mapOfIndicators.values()。stream()
.flatMap(Collect ion :: stream)
.filter(objectDTO - > !)()()()()()()())()()()()()()() :: parseDouble))));
-
过滤结果:
地图< String,Double> (b)收集器集合(b)(ObjectDTO :: getCountryName,$ b $) b)Collectors.mapping(ObjectDTO :: getNewIndex,Collectors.averagingDouble(
s-> s.isEmpty()?Double.NaN:Double.parseDouble(s)))),
m-> (m.values()。removeIf(d-> Double.isNaN(d)); return m;}));
I have a map of the format (reference to Finding average using Lambda (Double stored as String))
Map<String, Double> averages=mapOfIndicators.values().stream()
.flatMap(Collection::stream)
.filter(objectDTO -> !objectDTO.getNewIndex().isEmpty())
.collect(Collectors.groupingBy(ObjectDTO::getCountryName,
Collectors.mapping(ObjectDTO::getNewIndex,
Collectors.averagingDouble(Double::parseDouble))));
I would like to ignore the ignore the entire country mapping even if one of them is newIndex value for that country is empty?
Since Collectors.groupingBy
does not allow to skip groups, you either have to analyze the filtering condition in advance so you can filter before performing groupBy
or filter the map afterwards (I ignore the third option, implement your own groupingBy
collector.
Analyze in advance:
Map<String, Boolean> hasEmpty=mapOfIndicators.values().stream() .flatMap(Collection::stream) .collect(Collectors.groupingBy(ObjectDTO::getCountryName, Collectors.mapping(o->o.getNewIndex().isEmpty(), Collectors.reducing(false, Boolean::logicalOr)))); Map<String, Double> averages=mapOfIndicators.values().stream() .flatMap(Collection::stream) .filter(objectDTO -> !hasEmpty.get(objectDTO.getCountryName())) .collect(Collectors.groupingBy(ObjectDTO::getCountryName, Collectors.mapping(ObjectDTO::getNewIndex, Collectors.averagingDouble(Double::parseDouble))));
Filter the result:
Map<String, Double> averages=mapOfIndicators.values().stream() .flatMap(Collection::stream) .collect(Collectors.collectingAndThen( Collectors.groupingBy(ObjectDTO::getCountryName, Collectors.mapping(ObjectDTO::getNewIndex, Collectors.averagingDouble( s->s.isEmpty()? Double.NaN: Double.parseDouble(s)))), m->{ m.values().removeIf(d->Double.isNaN(d)); return m; }));
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