CODEWITHSUNDEEP
javaarraylistdata-structures
luksmir
luksmir

Reputation: 3154

Fast aggregation of multiple ArrayLists into a single one

I have the following list:

List<ArrayList> list;

list.get(i) contains the ArrayList object with the following values {p_name=set1, number=777002}.

I have to create a 

Map<key,value>

where the key contains the p_name, and values are the numbers.

How to do it easily and fast as there can be hundreds of entries in the initial list and each number can be present in multiple p_name entries.

Update: Here is my current solution

 List<Row> list; //here is my data

    Map<String,String> map = new TreeMap<String,String>();

    for (Row l : list) {
        if (l.hasValues()) {
            Map<String, String> values = l.getResult(); // internal method of Row interface that returns a map
            String key = values.get( "number");
            map.put(key,  values.get( "p_name" ));
        }  
    }

The method works, but maybe it could be done better?

PS : There is an obvious error in my design. I wonder if you find it :)

Upvotes: 2

Views: 89

Answers (1)

Eugene
Eugene

Reputation: 120968

Sine the key can have more then one values, what you are looking for is a MultiMap. Multimap Or a simple map in the form

  Map<Key,ArrayList<Values>>

There is no "fast" way here to me. You still need to iterate through all the elements and check all the values.

And actually hundreds to Java is not much at all

Upvotes: 1

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