Question

I have a large Set<String> that contains many words, say:

“aaa, cCc, dDD, AAA, bbB, BBB, AaA, CCc, …”

I want to group all duplicate words from the Set ignoring the case sensitivity of the words then save them in a Vector<Vector<String>> or whatever, so each Vector<String> item will contain the group of similar words, like this :

Vector<String>: aaa, AAA, AaA, …

Vector<String>: cCc, CCc, …

Vector<String>: bbB, BBB, …

I care about the performance as this Set contain many words.

Answer 1

I would create a HashMap<String, Vector<String>> hashMap.
Next, for each ‘string’ in your set

if (!hashMap.containsKey(string.toLowerCase()){
     Vector v = new Vector();
     v.add(string);
      hashMap.put(string.toLowerCase(), v);
} else { 
     hashMap.get(string.toLowerCase()).add(string);
}

At the end, create a Vector of vectors if needed, or work with the hashmap.valueSet()