Sort a Map in descending order based on value of arraylist in Java

Question

I have a Map of type

static Map<String, ArrayList<String>> Container = new HashMap<String, ArrayList<String>>();

The value array list has two elements, the first index is an extension and the second is size,

Container : {
C:\HTML\viewer\files\output\ViewerJS\commons-io-2.11.0-src (2).zip=[zip, 919362], 
C:\HTML\viewer\files\jar_files (2).zip=[zip, 345068], 
C:\HTML\viewer\files\output\ViewerJS\rar1.rar=[rar, 1], 
C:\HTML\viewer\files\output\files.zip=[zip, 10184010], 
C:\HTML\viewer\files\check2.zip=[zip, 1]
}

I want the map to be sorted in descending order based on the number in index 1 of the map value which is the size which is also of type STRING.

A little help would be much appreciated, Thank you.

hope this link will help you stackoverflow.com/questions/18881182/… — deepakrajbhar
– deepakrajbhar, Commented Feb 23, 2022 at 6:40

Nowhere Man · Accepted Answer · 2022-02-23 07:06:21Z

TreeMap can be sorted by keys, and LinkedHashMap maintains the insertion order.

Most likely, you need just to sort the output of the map contents in the desired order, which can be implemented like this using simple Comparator.comparing and Comparator.reverseOrder():

Container.entrySet()
    .stream()
    .sorted(Comparator.comparing(
        e -> Long.parseLong(e.getValue().get(1)), Comparator.reverseOrder()
    ))
    .forEach(System.out::println);

Output:

C:\HTML\viewer\files\output\files.zip=[zip, 10184010]
C:\HTML\viewer\files\output\ViewerJS\commons-io-2.11.0-src (2).zip=[zip, 919362]
C:\HTML\viewer\files\jar_files (2).zip=[zip, 345068]
C:\HTML\viewer\files\check2.zip=[zip, 1]
C:\HTML\viewer\files\output\ViewerJS\rar1.rar=[rar, 1]

Or the results of sorting may be re-collected into a LinkedHashMap (example of using Map.Entry.comparingByValue):

Container = Container.entrySet()
    .stream()
    .sorted(Map.Entry.comparingByValue(Comparator.comparing(
        arr -> Long.parseLong(arr.get(1)), Comparator.reverseOrder()
    )))
    .collect(Collectors.toMap(
        Map.Entry::getKey,
        Map.Entry::getValue,
        (a, b) -> a,
        LinkedHashMap::new
    ));

Victor · Accepted Answer · 2022-02-24 02:51:11Z

This uses a TreeMap and a utility function(addElementsToMap) that would update your map.

Note: A Comparator is provided at map creation time.

public class DriverClass {


private static Map<Integer, ArrayList<String>> container = new TreeMap<>((o1, o2) -> (o2 < o1) ? -1 : 1);

public static void main(String[] args) {
    DriverClass driver = new DriverClass();
    String[] elementsList = driver.collectElements();
    driver.addElementsToMap(elementsList);
    container.entrySet().forEach(e -> System.out.println(e.getKey() + " ----- " + e.getValue()));

}

private void addElementsToMap(String[] elementsList) {
     int i = 0;
    for (int j = elementsList.length/2; j <= elementsList.length-1; j++) {
       int size = Integer.parseInt(elementsList[i+1].replaceAll("]", ""));
        container.put(size, new ArrayList<>(Arrays.asList(elementsList[i], elementsList[i+1])));
        i += 2;
    }
}

private String[] collectElements() {
    return new String[] {
        "C:\\HTML\\viewer\\files\\output\\ViewerJS\\commons-io-2.11.0-src (2).zip=[zip", "919362]",
        "C:\\HTML\\viewer\\files\\jar_files (2).zip=[zip", "345068]",
        " C:\\HTML\\viewer\\files\\output\\ViewerJS\\rar1.rar=[rar", "1]",
        "C:\\HTML\\viewer\\files\\output\\files.zip=[zip", "10184010]",
        "C:\\HTML\\viewer\\files\\check2.zip=[zip", "1]"};
 }
}

outputs:

10184010 ----- [C:\HTML\viewer\files\output\files.zip=[zip, 10184010]]
919362 ----- [C:\HTML\viewer\files\output\ViewerJS\commons-io-2.11.0-src (2).zip=[zip, 919362]]
345068 ----- [C:\HTML\viewer\files\jar_files (2).zip=[zip, 345068]]
1 ----- [C:\HTML\viewer\files\check2.zip=[zip, 1]]
1 ----- [ C:\HTML\viewer\files\output\ViewerJS\rar1.rar=[rar, 1]]

I noticed that I did not account for duplicate keys. I updated compare(Integer o1, Integer o2) return expression to include duplicate keys.

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