Sorting HashMap<String, String> with integers as Strings

Question

I'm trying to sort my HasMap ArrayList so my listview is sorted by values but I'm not getting it. Basically I have several keys and one of them is "type" which holds values like "1", "4", "3",....

I want to order the list by this key "type" but I'm getting "1", "11", "2" instead of "1", "2", "11"...

I'm trying this code to sort it:

Collections.sort(myList, new Comparator<HashMap<String, String>>() {
public int compare(HashMap<String, 
String> mapping1,HashMap<String, String> mapping2) {
return mapping1.get("type").compareTo(mapping2.get("type"));
    }
});

Why are you using a String for the key, when you're using it purely to store ints? — anotherdave
– anotherdave, Commented Apr 15, 2013 at 7:47
There's more keys in there that aren't ints. When I try to change that key to int I get an error on my map.put(key,value) — bond
– bond, Commented Apr 15, 2013 at 8:09
In that case, beware of NumberFormatException that will get thrown by your accepted answer - you'll need to expand this logic to accommodate your valid String keys. docs.oracle.com/javase/1.5.0/docs/api/java/lang/… — anotherdave
– anotherdave, Commented Apr 15, 2013 at 9:44

Santosh · Accepted Answer · 2013-04-15 06:54:50Z

5

Your type is a String and thats why you are getting "1", "11", "2". Convert that string to integer (Integer.valueOf()) and then compare.

change the following

mapping1.get("type").compareTo(mapping2.get("type"));

to

 Integer.valueOf(mapping1.get("type")).compareTo(Integer.valueOf(mapping2.get("type")));

Note: I did not compile the above code.

answered Apr 15, 2013 at 6:54

Santosh

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sanbhat · Accepted Answer · 2013-04-15 06:51:37Z

1

The data-type of "type" seems to be String. Hence the sorting "1", "11", "2" seems correct. Change the data-type of "type" to Integer

OR

in compare method compare Integer.parseInt values of the "type"

answered Apr 15, 2013 at 6:51

sanbhat

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Comments

anotherdave · Accepted Answer · 2013-04-15 17:28:04Z

You'll need to handle non-integer values in your comparator, if, as you mentioned above, you expect to have a mixture of String and Integer keys.

Collections.sort(myList, new Comparator<HashMap<String, String>>() {
    public int compare(HashMap<String, String> mapping1,
                       HashMap<String, String> mapping2) {
        String valueOne = mapping1.get("type");
        String valueTwo = mapping2.get("type");
        try {
            return Integer.valueOf(valueOne).compareTo(Integer.valueOf(valueTwo));
        } catch(NumberFormatException e) {
            return valueOne.compareTo(valueTwo);
        }
    }
});

(Otherwise, the key value should be changed to Integer to avoid mistakes by other developers.)

RUTURAJ Raval · Accepted Answer · 2016-01-01 19:48:26Z

0

You can do as below..

Change parameter as per your need..

Set<Entry<String, Integer>> set = map.entrySet();
        List<Entry<String, Integer>> list = new ArrayList<Entry<String, Integer>>(set);
        Collections.sort( list, new Comparator<Map.Entry<String, Integer>>()
        {
            public int compare( Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2 )
            {
                return (o2.getValue()).compareTo( o1.getValue() );
            }
        } );
        for(Map.Entry<String, Integer> entry:list){
            System.out.println(entry.getKey()+" ==== "+entry.getValue());
        }

answered Jan 1, 2016 at 19:48

RUTURAJ Raval

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