How to group array elements and get many occurring elements?

Question

How to get an element of an array that occur multiple times?

ArrayList<String> arrBarCode = new ArrayList<String>();
arrBarCode.add(BarCode);

I have no idea what you're asking about. Do you mean how to get the frequency of a certain barcode in the list, e.g. something like `Map`? If so, what did you try so far? — Thomas, Mar 12 '20 at 13:30
Yes, right. I want to get the frequency of a particular barcode in the list. — embarcadero, Mar 12 '20 at 13:35

score 0 · Answer 1 · answered Mar 12 '20 at 13:38

Use a Map<String, Integer> to remember the number of occurrences while iterating over the List:

ArrayList<String> arrBarCode = new ArrayList<String>();
arrBarCode.add("a");
arrBarCode.add("a");
arrBarCode.add("a");
arrBarCode.add("c");
Map<String, Integer> a = new HashMap<>();
arrBarCode.forEach(s -> a.put(s, a.computeIfAbsent(s, foo -> 0)+1));
System.out.println(a);

prints

{a=3, c=1}

How to group array elements and get many occurring elements?

1 Answers1