Trying to use a Hashmap<Integer, Integer>

Question

how would I increment the key [i] by 1 in this situation every time I run through this for loop with the way I currently have it set up all the elements only get mapped to 1. I am trying to find out how many times each number occurs. I have tried +1 in the empty spot after list.get(i) but again only maps each element to 1. thank you.

    List<Integer> list = new ArrayList<Integer>();
    HashMap<Integer,Integer> Mode = new HashMap<Integer, Integer>();
    for (int i = 0; i < arr.length; i++) {
        for (int j = 0; j < arr[i].length; j++) {
            list.add(arr[i][j]); 
        }
    }
    System.out.println(list);
    int count = 1;
    for(int i = 0; i < list.size(); i ++) {
        Mode.put(list.get(i), );

Your question is not very understandable, but comment is good — Kushan
– Kushan, Commented Jan 20, 2012 at 4:00
haha sorry been working on these assignments since 10AM MT time just out of it thanks for the help I really appreciate it — Kristopher
– Kristopher, Commented Jan 20, 2012 at 4:21

KV Prajapati · Accepted Answer · 2012-01-20 03:44:24Z

3

You need to specify a Key here.

for(int i = 0; i < list.size(); i++) {
        int value=list.get(i);
        if(!Mode.containsKey(value))
            Mode.put(value,1);
        else
            Mode.put(value,Mode.get(value)+1);
}

edited Jan 20, 2012 at 3:44

answered Jan 20, 2012 at 3:31

KV Prajapati

94.8k20 gold badges151 silver badges188 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Eric B. Over a year ago

@AVD is right on the money. Or your question is unclear. From what I understand, you are looking to count the number of occurances a value occurs within your array. Consequently, you use the value as the key to your map, and then the number of occurances as the map value. That is precisely what is being suggested. If this is incorrect, please clarify your question and explain why the solution offered is invalid.

Kushan · Accepted Answer · 2012-01-20 04:01:56Z

2

According to your comment,

for(int i = 0; i < list.size(); i ++) {
   if(Mode.containsKey(list.get(i)) ){
       Integer count = Mode.get(list.get(i));

       Mode.put(list.get(i), ++count);}
   else
       Mode.put(list.get(i), 1);

edited Jan 20, 2012 at 4:01

answered Jan 20, 2012 at 3:31

Kushan

10.7k4 gold badges39 silver badges41 bronze badges

Comments

Louis Wasserman · Accepted Answer · 2012-01-20 04:26:21Z

1

If you have the option, you may find it easier to use something like Multiset from Guava.

Multiset<Integer> seen = HashMultiset.create();
for (int[] row : arr) {
  for (int elem : row) {
    seen.add(elem); // none of that nasty dealing with the Map
  }
}
// you can look up the count of an element with seen.count(elem)
E mostCommon = null;
int highestCount = 0;
for (Multiset.Entry<Integer> entry : seen.entrySet()) {
  if (entry.getCount() > highestCount) {
    mostCommon = entry.getElement();
    highestCount = entry.getCount();
  }
}
return mostCommon; // this is the most common element

answered Jan 20, 2012 at 4:26

Louis Wasserman

200k26 gold badges367 silver badges437 bronze badges

1 Comment

Louis Wasserman Over a year ago

If you can't use third-party libraries -- which may be the case, if this is a homework assignment -- you should use AVD's solution.

Collectives™ on Stack Overflow

Trying to use a Hashmap<Integer, Integer>

3 Answers 3

1 Comment

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related