I have list of data with amount, I want to separate duplicate data with that count and that total amount.

ArrayList<String> al=new ArrayList<String>();
al.add("aa-10.00");
al.add("bb-15.00");
al.add("aa-20.00");
al.add("aa-30.00");
al.add("bb-10.00");

Output data amount count
        aa  60.00    3
        bb  25.00    2

CodePudding user response：

The ideas for dealing with this problem are as follows:

1. Split each character string into a name and a value.
2. Collect statistics on each character string. Sum up and count the characters with the same name.
3. Store the result in the map.
4. Print the statistics result.

ArrayList<String> al=new ArrayList<>();
al.add("aa-10.00");
al.add("bb-15.00");
al.add("aa-20.00");
al.add("aa-30.00");
al.add("bb-10.00");

// Map<data name such as "aa", Pair<sum, count> >
Map<String, Pair<Double, Integer>> result = new HashMap<>();
al.forEach(record -> {
    // split data by "-", and split aa-10.00 to "aa" and "10.00"
    String [] splitRecord = record.split("-");
    // if already exsit, sum and cardinality
    if (result.containsKey(splitRecord[0])) {
        result.put(splitRecord[0], new Pair<>(Double.valueOf(splitRecord[1])   result.get(splitRecord[0]).first(), result.get(splitRecord[0]).second()   1));
    } else {
        result.put(splitRecord[0], new Pair<>(Double.valueOf(splitRecord[1]), 1));
    }
});

System.out.println(result);

CodePudding user response：

Since release of Java 8 back in March 2014, Java provides Stream API which allows group by elements of collections and collect some statistical data.

So, the input strings should be split into parts: name and amount separated with dash -, grouped by String name, and statistics should be collected for double amount.

Using Collection::stream, String::split, Collectors.groupingBy (with the Supplier and downstream collector), Collectors.summarizingDouble returning the DoubleSummaryStatistics the following solution can be implemented:

List<String> al = Arrays.asList(
    "aa-10.00", "bb-15.00", "aa-20.00", "aa-30.00", "bb-10.00"
);

Map<String, DoubleSummaryStatistics> stats = al
    .stream()
    .map(s -> s.split("-")) // Stream<String[]>
    .collect(Collectors.groupingBy(
        arr -> arr[0],
        LinkedHashMap::new,
        Collectors.summarizingDouble(arr -> Double.parseDouble(arr[1]))
    ));

System.out.println("data  amount  count");
stats.forEach((name, stat) -> System.out.printf("%4s  %6.2f  =%n", 
    name, stat.getSum(), stat.getCount()
));

Output:

data  amount  count
  aa   60.00    3
  bb   25.00    2

LinkedHashMap ensures that the elements appear in the insertion order (as they appeared in the input list).