CODEWITHSUNDEEP
androidstringsortingarraylisthashmap
Ovidiu Birgu
Ovidiu Birgu

Reputation: 439

How to sort HashMap<String, String[]> by String in android

I have this code: 

    HashMap<String, String[]> unsorted = new HashMap<String, String[]>();
    String[] values = new String[3];
    String key;

    //add data to hashmap
    key = "abc";
    values[0] = "a"; values[1]="b"; values[2]="c";
    unsorted.put(key, values);

    key = "abc";
    values[0] = "aa"; values[1]="bb"; values[2]="cb";
    unsorted.put(key, values);

    key = "def";
    values[0] = "d"; values[1]="e"; values[2]="f";
    unsorted.put(key, values);

    //sort hashmap
    /***********/

    //output should be:
    { abc-[a,b,c], abc-[aa,bb,cc], def-[d,e,f] }

    //or

    { abc-[aa,bb,cc], abc-[a,b,c], def-[d,e,f] }

How can I sort it like that? Note: I tried with using TreeMap, and other examples, but they eliminate the elements where the keys are equal.

Edit: I solved my problem :) thanks to Guillaume. Here is what I used:

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

public class test {

public static void main(String[] args) {

    ArrayList<CustomObject> objs = new ArrayList<CustomObject>();

    objs.add(new CustomObject("abc", new String[] {"a", "b", "c"}));
    objs.add(new CustomObject("def", new String[] {"d", "e", "f"}));
    objs.add(new CustomObject("abc", new String[] {"aa", "bb", "cc"}));


    System.out.println(objs.isEmpty());

    Collections.sort(objs, new Comparator<CustomObject>() {
        @Override
        public int compare(CustomObject o1, CustomObject o2) {
            int i = o1.getKey().compareTo(o2.getKey());
            if(i == 0)
                return -1;
            return i;
        }
    });

    for(int i=0; i<objs.size(); i++)
        System.out.println("key/value pair:" + objs.get(i).getKey() + " - " + objs.get(i).getValues()[0]);
    }
}

And the CustomObject:

public class CustomObject {

private String key;
private String[] values;

public CustomObject(String key, String[] values) {
    this.key = key;
    this.values = values;
}

public String getKey() {
    return key;
}

public String[] getValues() {
    return values;
}
}

Upvotes: 3

Views: 14793

Answers (4)

Dashrath Rathod
Dashrath Rathod

Reputation: 538

You can also sort your hashmap using following method 

private static HashMap sortByValues(HashMap map) {
        List list = new LinkedList(map.entrySet());
        // Defined Custom Comparator here
        Collections.sort(list, new Comparator() {
            public int compare(Object o1, Object o2) {
                return ((Comparable) ((Map.Entry) (o1)).getValue())
                        .compareTo(((Map.Entry) (o2)).getValue());
            }
        });

        // Here I am copying the sorted list in HashMap
        // using LinkedHashMap to preserve the insertion order
        HashMap sortedHashMap = new LinkedHashMap();
        for (Iterator it = list.iterator(); it.hasNext();) {
            Map.Entry entry = (Map.Entry) it.next();
            sortedHashMap.put(entry.getKey(), entry.getValue());
        }
        return sortedHashMap;
    }

call method like //shift your hashmap

 shift =sortByValues(shift)

Upvotes: 1

Guillaume
Guillaume

Reputation: 22822

If you need special ordering, and the ability to have multiple objects that have an equal "key", that screams for List, with a custom Comparator.

1- Define a class of elements to store in your list. In your case, it's an object that has 2 fields: a "key" and an array of String. Let's call it CustomObject (you can call it as you like)

2- Stick all your objects in the list

Like that:

list.add(new CustomObject("abc", new String[] {"a", "b", "c"});
list.add(new CustomObject("abc", new String[] {"aa", "bb", "cc"});
list.add(new CustomObject("def", new String[] {"d", "e", "f"});

3- Order your list using a custom comparator.

To order the list do

Collections.sort(list, new Comparator<CustomObject>() {
        @Override
        public int compare(CustomObject o1, CustomObject o2) {
            return o1.getArray().compare(o2.getArray());
        }
    });

(your comparator needs to be a bit more sophisticated, to properly compare arrays, but you see my point).

An alternative to that is to add a natural ordering to your CustomObject (implements Comparable), and stick them into a TreeSet.

Upvotes: 5

Jave
Jave

Reputation: 31846

The HashMap can not be sorted (or contain duplicate keys), it is part of how it is implemented (see the documentation).

This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time.

So you better do as other people are suggesting and switch to a list or a different map implementation.

Upvotes: 3

Thomas Johan Eggum
Thomas Johan Eggum

Reputation: 915

You need to use a Map that allows duplicate keys, there is no such Map in the JDK. Try using a Multimap in Google guava. http://google-collections.googlecode.com/svn/trunk/javadoc/com/google/common/collect/Multimap.html

An implementation that have natural order is the TreeMultiMap: http://google-collections.googlecode.com/svn/trunk/javadoc/com/google/common/collect/TreeMultimap.html

Good luck :)

Upvotes: 0

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