Finding the n largest values in a hashmap

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Iterate through a HashMap [duplicate] 7 answers

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Probably this is not the most efficient way to do, but it should solve your problem:

static HashMap<String, Integer> nLargest(HashMap<String, Integer> map, int n) { //map and n largest values to search for

    Integer value;
    ArrayList<String> keys = new ArrayList<>(n); //to store keys of the n largest values
    ArrayList<Integer> values = new ArrayList<>(n); //to store n largest values (same index as keys)
    int index;
    for (String key : map.keySet()) { //iterate on all the keys (i.e. on all the values)
        value = map.get(key); //get the corresponding value
        index = keys.size() - 1; //initialize to search the right place to insert (in a sorted order) current value within the n largest values
        while (index >= 0 && value > values.get(index)) { //we traverse the array of largest values from smallest to biggest
            index--; //until we found the right place to insert the current value
        }
        index = index + 1; //adapt the index (come back by one)
        values.add(index, value); //insert the current value in the right place
        keys.add(index, key); //and also the corresponding key
        if (values.size() > n) { //if we have already found enough number of largest values
            values.remove(n); //we remove the last largest value (i.e. the smallest within the largest)
            keys.remove(n); //actually we store at most n+1 largest values and therefore we can discard just the last one (smallest)
        }
    }
    HashMap<String, Integer> result = new HashMap<>(values.size());
    for (int i = 0; i < values.size(); i++) { //copy keys and value into an HashMap
        result.put(keys.get(i), values.get(i));
    }
    return result;
}

I hope this will help you.

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