CODEWITHSUNDEEP
javaobjectdictionaryhashmap
Eme Emertana
Eme Emertana

Reputation: 571

how to sort items of a MAP and remove one?

I am using the following code to keep list of objects in a MAP,

 Map<String, List<Rows>> map = new HashMap<String, List<Rows>>()
 while( rs.next() ) {
      Rows row = new Rows();
      /*
       * code to initialize the values of row from the record
      */
     String category = rs.getString("Cat");
     if(!map.containsKey(category)){
         map.put(category, new ArrayList<Rows>());
     }
     map.get(category).add(row);
  }

is it possible to sort the values for each category? how to remove an item in a specific category?

Upvotes: 0

Views: 1077

Answers (4)

Mukul Goel
Mukul Goel

Reputation: 8465

use list to store items in ur categories. thers an API function to sort list. and use (map.remove(category) ).get(0) to get first item in ur category list

Upvotes: 0

AlexR
AlexR

Reputation: 115398

To remove item use remove() method of map:

map.remove(category)

As far as I understand items of each category are stored in list, so sorting is simple:

Collections.sort(map.get(category))

You can customize your sorting using your custom Comparator.

EDIT:

If however you wish to sort keys into your map you have to use SortedMap, e.g. TreeMap and probably provide your comparator that knows to compare your categories. Otherwise keys will be sorted alphabetically.

Upvotes: 1

Usman Ismail
Usman Ismail

Reputation: 18689

Is it possible to sort values in the category: Use PriorityQueue instead of list to keep values sorted as they are added.

To remove you can use map.get(category).remove(row); Or create a new class that inherits from map and overrides remove(..). You can put code here to remove from the list attached to a specific key rather than the map itself.

Upvotes: 0

RAS
RAS

Reputation: 8156

@Eme If you want a map that is sorted by its key, it is called SortedMap.

Besides if you want to remove one of the item from the List for a particular category, you can do the following:

List<Row> list = map.get(category);
list.remove(index of element you want to remove);
map.put(category, list);

Upvotes: 1

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