CODEWITHSUNDEEP
javahashmap
GustyWind
GustyWind

Reputation: 3036

How to rearrange the items in a map based on another map keys

Hi I had a requirement where objects of a map are to arranged in order of keys of another map. here is the map

Map ObjectMap = new HashMap()
ObjectMap .put(id1,Obj1);
ObjectMap .put(id2,Obj2);
ObjectMap .put(id3,Obj3);
ObjectMap .put(id4,Obj4);

Now a rank map decides the order of ids in ObjectMap 

Map rankedMap = new HashMap()

rankedMap .put(rank1,id3);
rankedMap .put(rank2,id4);
rankedMap .put(rank3,id1);
rankedMap .put(rank4,id2);

Now I have to arrange the ObjectMap objects accoding to the rank of each ids like

ObjectMap .put(id3,Obj1);
ObjectMap .put(id4,Obj2);
ObjectMap .put(id1,Obj3);
ObjectMap .put(id2,Obj4);

ids are Long objects

ranks are int objects

Please help Thanks in advance

Upvotes: 1

Views: 1633

Answers (3)

Fortega
Fortega

Reputation: 19682

The 'rankedMap' should be a linked map, as said above:

Map rankedMap = new LinkedHashMap()

rankedMap .put(rank1,id3);
rankedMap .put(rank2,id4);
rankedMap .put(rank3,id1);
rankedMap .put(rank4,id2);

next, you can iterate over the ids in the rankedMap to fill the rankedObjectMap, which is also a linkedHashMap: (code not tested)

Map rankedObjectMap = new LinkedHashMap();
for(Object id : rankedMap.values()){
  rankedObjectMap.put(id, objectMap.get(id));
}

Upvotes: 2

hovanessyan
hovanessyan

Reputation: 31463

You can try with TreeMaps and custom Comparators.

Upvotes: 1

amit
amit

Reputation: 178471

HashMap has no defined ordering. If you want ordering, and still benefit the O(1) seek time the HashMap offers, you might want to use LinkedHashMap, but note that ordering in this map is defined by order of insertions. You will have to take care of it by inserting your elements in order.

Upvotes: 1

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