Java 8 Stream groupingby

Question

I have List<Map<String, String>> each item in the list is a map e.g

companyName - IBM firstName - James country - USA ... 

I would like create a Map<String, List<String>> where it maps companyName to a list of of firstName e.g

IBM -> James, Mark ATT -> Henry, Robert..   private Map<String,List<String>> groupByCompanyName(List<Map<String, String>> list) {     return list.stream().collect(Collectors.groupingBy(item->item.get("companyName"))); } 

but this will create Map<String, List<Map<String, String>> (mapping comanyName to a list of maps)

how to create a Map<String, List<String>>?

Answer 1

Haven't tested it, but something like this should work:

Map<String, List<String>> namesByCompany     = list.stream()           .collect(Collectors.groupingBy(item->item.get("companyName"),                    Collectors.mapping(item->item.get("firstName"), Collectors.toList())));