I have an arraylist 'response' with each element containing an object Meta and List(Values) ie a list which contains nested list and some meta data for each nested list. I would like to use stream() on this to create a new list. The new list will contain all the value objects and its corresponding meta data. How can i use response.stream() to accomplish this?
//Input
Meta meta1 = new Meta("name1");
Meta meta2 = new Meta("name2");
Meta meta3 = new Meta("name3");
List<Values> values1 = new ArrayList<>();
values1.add(new Values("1 Aug", 1.0F));
values1.add(new Values("2 Aug", 2.0F));
values1.add(new Values("3 Aug", 3.0F));
List<Values> values2 = new ArrayList<>();
values2.add(new Values("1 Aug", 4.0F));
values2.add(new Values("2 Aug", 5.0F));
values2.add(new Values("3 Aug", 6.0F));
List<Values> values3 = new ArrayList<>();
values3.add(new Values("1 Aug", 7.0F));
values3.add(new Values("2 Aug", 8.0F));
values3.add(new Values("3 Aug", 9.0F));
Response response1 = new Response(meta1, values1);
Response response2 = new Response(meta2, values2);
Response response3 = new Response(meta3, values3);
List<Response> response = new ArrayList<>();
response.add(response1);
response.add(response2);
response.add(response3);
//use response.stream()...
//output
List<MetaValue> metaValueList = new ArrayList<>();
metaValueList.add(new MetaValue("name1", "1 Aug", 1.0F));
metaValueList.add(new MetaValue("name1", "2 Aug", 2.0F));
metaValueList.add(new MetaValue("name1", "3 Aug", 3.0F));
metaValueList.add(new MetaValue("name2", "1 Aug", 4.0F));
metaValueList.add(new MetaValue("name2", "2 Aug", 5.0F));
metaValueList.add(new MetaValue("name2", "3 Aug", 6.0F));
metaValueList.add(new MetaValue("name3", "1 Aug", 7.0F));
metaValueList.add(new MetaValue("name3", "2 Aug", 8.0F));
metaValueList.add(new MetaValue("name3", "3 Aug", 9.0F));
You need to stream the responses and flatMap the values. I'll take some liberty with the naming because you haven't provided class definitions, but this should give you an idea:
List<MetaValue> metaValueList = response.stream()
.flatMap(r -> r.getValues()
.stream()
.map(v -> new MetaValue(r.getMeta().getName(), v.getDate(), v.getValue())))
.collect(Collectors.toList());
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