Using HashMap for getting repeating occurences

Question

I have a HashMap which is populated with String and Integer:

Map<String, Integer> from_table;
from_table = new HashMap<String, Integer>();

Next i want to get all the keys of items which there value (the Integer) is above x.

For example all the keys which their value is over 4.

Is there a fast method for doing that?

Thnaks!

Nothing faster than a loop unless you use a sorted version of hashmap. — selig, Jun 24 '13 at 19:35
What is the sorted version? can i define sorted version with String and an Integer? — Michael A, Jun 24 '13 at 19:37
It's either sorting, looping or, if you're in to spare some extra memory, having an extra map where for "the other way around" (`Map`) — Fritz, Jun 24 '13 at 19:38
[This question](http://stackoverflow.com/questions/780541/how-to-sort-hash-map) is relevant. — selig, Jun 25 '13 at 12:50

score 1 · Accepted Answer · edited Jun 24 '13 at 21:53

1

public static void printMap(Map mp) {
    for(Map.Entry pairs : mp.entrySet()) {
        if(pairs.getValue() >= 4)
        {
          System.out.println(pairs.getKey());
        }
    }
}

edited Jun 24 '13 at 21:53

Jim Garrison

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answered Jun 24 '13 at 19:37

orangegoat

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score 0 · Answer 2 · answered Jun 24 '13 at 19:38

Well, iterate over the key-value pairs and collect keys where values meet the criteria

//collect results here
List<String> resultKeys= new ArrayLIst<String>();

//hash map iterator
Iterator<String> it = from_table.keySet();
while(it.hasNext()) {
    //get the key
    String key= it.next();
    /get the value for the key
    Integer value= from_map.get(key);
    //check the criteria
    if (value.intValue() > x) {
        resultKeys.add(key);
    }
}

score 0 · Answer 3 · answered Jun 24 '13 at 19:39

0

Not in standard Java. Guava has method called filter doing exactly this as a one-liner (+ the predicate).

answered Jun 24 '13 at 19:39

Jiri Kremser

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score 0 · Answer 4 · answered Jun 24 '13 at 19:39

0

As the above solution states there is nothing faster than just looping through, but an alternative solution would be to edit the function to put something in the map and have it check if there are 4 or more items, if there are it adds it to a new list with only objects with a count of more than 4

answered Jun 24 '13 at 19:39

aaronman

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Umm... count has nothing to do with it. Please re-read the question. – Jim Garrison Jun 24 '13 at 21:52
@JimGarrison I meant value I just assumed it was a count – aaronman Jun 25 '13 at 01:07

Using HashMap for getting repeating occurences

4 Answers4