Sorting the data in increasing order based on keys in Multimap Google Guava

Question

I created a Multimap

Multimap<Integer, String> mhm= ArrayListMultimap.create();

my numbers range from 0 to 2400.

I have inserted data like

 mhm.put(800 ,"A")
 mhm.put(1200 ,"B")
 mhm.put(1200 ,"A")
 mhm.put(1500 ,"B")
 mhm.put(600 ,"A")
 mhm.put(700 ,"B")
 mhm.put(1200 ,"A")
 mhm.put(1201 ,"B")

I want to sort the Multimap on key field that is Integer? There are not much posts on satckoverflow which tells how to do this.

expected output:

 mhm.put(600 ,"A")
 mhm.put(700 ,"B")
 mhm.put(800 ,"A")
 mhm.put(1200 ,"B")
 mhm.put(1200 ,"A")
 mhm.put(1200 ,"A")
 mhm.put(1201 ,"A")
 mhm.put(1500 ,"B")

Please note that the expected output is sorted only on key. If two keys have same value then the key which appeared first should come first. how to enforce this? Is this case automatically taken care when we sort the Multimap on keys?

This is not homework question, trying to play around Google Guava.

duplicate http://stackoverflow.com/questions/5501468/having-a-multimap-sorted-on-keys-only-in-java — Amir Afghani, Dec 02 '13 at 18:31
@S.SWAIN I just finished my semester exams. trying to prepare for placements. I am not that good at java. I need some help in solving it. — user3058364, Dec 02 '13 at 18:37

Grzegorz Rożniecki · Accepted Answer · 2015-12-07T12:46:54.303

6

You want keys in natural order - just use custom Multimap using newListMultimap from Multimaps class:

ListMultimap<Integer, String> mhm = Multimaps.newListMultimap(
  new TreeMap<Integer, Collection<String>>(),
  new Supplier<List<String>>() {
    public List<String> get() {
      return Lists.newArrayList();
    }
  });

In Java 8 it's shorter:

ListMultimap<Integer, String> mhm = Multimaps.newListMultimap(
    new TreeMap<>(), ArrayList::new);

But if you're using Guava 16+ (and you should now), you can use MultimapBuilder which is even more clean:

ListMultimap<Integer, String> mhm = MultimapBuilder.treeKeys().arrayListValues().build();

Because you can think of multimap as map key -> collection, just use JDK's TreeMap which is sorted according to the natural ordering of its keys.

Example:

mhm.put(2, "some");
mhm.put(1, "value");
mhm.put(2, "here");
System.out.println(mhm.toString());
// { 1: [ "value" ], 2: [ "some", "here" ] }

edited Dec 07 '15 at 12:46

answered Dec 02 '13 at 18:35

Grzegorz Rożniecki

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I want them to be sorted in first place but if there are duplicate keys, then natural order should be maintained – user3058364 Dec 02 '13 at 18:41
1

It's Multimap, so if there are entries with duplicate keys put in the multimap, they'll be added to corresponding value collection (here: `List`). – Grzegorz Rożniecki Dec 02 '13 at 18:53
Thanks @Xaerxess for suggesting the MultimapBuilder – FakirTrappedInCode Dec 07 '15 at 13:08

score 5 · Answer 2 · answered Dec 02 '13 at 19:12

5

If you can use an immutable multimap, and don't need to mutate the multimap, then it's fairly simple:

new ImmutableListMultimap.Builder<Integer, String>
   .orderKeysBy(Ordering.natural())
   .putAll(multimap) // or put each entry
   .build();

answered Dec 02 '13 at 19:12

Louis Wasserman

191,574
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Sorting the data in increasing order based on keys in Multimap Google Guava

2 Answers2

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