Get the most common element of an Arraylist-CodePudding

I have an ArrayList from Type Cell. The ArrayList has values from Cells of an Excelsheet. I have tried different solutions from this site, but no one from them could was the right one. Thats why i have no Code to show you what i did. Almost every solution are for String.

I need to get the most common value in my ArrayList.

I tried to replace in the solutions the Strings with cell.getNumericValue() and change the Type of Double but it didnt worked.

Has anybody a solution for my problem?


Map<Cell, Long> f = dataaccx
                .stream()
                .collect(Collectors.groupingBy(v -> v, Collectors.counting()));
        Cell maxOccurence =
                Collections.max(f.entrySet(), Comparator.comparing(Map.Entry::getValue)).getKey();

        System.out.println(maxOccurence.getNumericCellValue());

Thats one Example what i tried. dataaccx is my Arraylist.

CodePudding user response：

You should group by the numeric value of the cell instead of the object itself.

Map<Double, Long> f = cells
        .stream()
        .collect(Collectors.groupingBy(Cell::getNumericCellValue, Collectors.counting()));
Map.Entry maxOccurence =
        Collections.max(f.entrySet(), Comparator.comparing(Map.Entry::getValue));
System.out.println(maxOccurence.getKey());

CodePudding user response：

If multiple most common values are possible and need to be printed, then it might be better to build the frequency map and find the maximal frequency in a single run using plain loop while building the map.

Stream API may be applied then to print the results.

int max = 0;
Map<Double, Integer> freqMap = new LinkedHashMap<>();
for (Cell c : cells) {
    int freq = freqMap.merge(c.getNumericCellValue(), 1, Integer::sum);
    if (freq > max) {
        max = freq;
    }
}
final int maxFreq = max; // max is not final and cannot be used in lambda below
freqMap.entrySet()
    .stream()
    .filter(e -> e.getValue() == maxFreq)
    .map(Map.Entry::getKey)
    .forEach(System.out::println);