Grouping in arrayList of arrayList

  • A+

Hi I have a String ArrayList of ArrayList. A sample is shown below:

  [[765,servus, burdnare],    [764,asinj, ferrantis],    [764,asinj, ferrantis],    [764,asinj, ferrantis],    [762,asinj, ferrantis],    [756,peciam terre, cisterne],    [756,peciam terre, cortile],    [756,peciam terre, domo],    [756,asinj, ferrantis]] 

Is it possible to get a list of unique values at index 1 for each value of index 0...The result I am expecting is:

765 - [servus] 764 - [asinj] 762 - [asinj] 756 - [peciam terre, asinj] 

I was trying a series of if statements however did not work


You can group by index-0 element and collect index-1 elements in a Set to get unique

List<List<String>> listOfList = ...//  Map<String, Set<String>> collect =         .filter(l -> l.size() >= 2)         .collect(Collectors.groupingBy(l -> l.get(0), Collectors.mapping(l -> l.get(1), Collectors.toSet()))); 


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