Using hash maps to create a table in Java

Question

I'm trying to create a program that lets you put any data into a table and you can perform functions like count how many words there are in a column, row etc. Is using a HashMap the best way to go about this?

If not what can you recommend?

At the moment I'm struggling to count each of the letters and it's adding 1 to each of the values each time giving a = 8, b and c = 0

public  void main(String[] args){
    map.put("0", "a");
    map.put("1", "b");
    map.put("2", "c");
    map.put("3", "a");
    map.put("4", "b");
    map.put("5", "a");
    map.put("6", "b");
    map.put("7", "c");

    for(Map.Entry ent : map.entrySet()){
        if(map.containsValue("a")){
        x++;}

        else if(map.containsValue("b")){
        y++;}

        else if(map.containsValue("c")){
        z++;}
    }

    System.out.println("a = " + x);
    System.out.println("b = " + y);
    System.out.println("c = " + z);

Maljam · Accepted Answer · 2016-04-03 22:56:42Z

1

Is using a HashMap the best way to go about this?

HashMap is a good way to go, but the way you are using it in your example is flawed because you can't simply count how many occurrences of a key are present.

So I suggest using HashMap<String, List<Integer>>, with List<Integer> keeping track of row indices:

    HashMap<String, List<Integer>> map = new HashMap<String, List<Integer>>();
    String[] strs = {"a", "b", "c", "a", "b", "a", "b", "c"};

    for(int i = 0 ; i < strs.length ; i++) {
        String s = strs[i];
        if(map.containsKey(s)) {
            map.get(s).add(i);
        } else {
            map.put(s, Arrays.asList(new Integer[]{i}));
        }
    }

    System.out.println("a = " + map.get("a").size());
    System.out.println("b = " + map.get("b").size());
    System.out.println("c = " + map.get("c").size());

edited Apr 3, 2016 at 22:56

answered Apr 3, 2016 at 22:47

Maljam

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2 Comments

Andrew Over a year ago

how to keep a number of a row?

Maljam Over a year ago

@AndrewTobilko Instead of Integer, you could use List<Integer> for indices of rows, and list.size() would be the number of occurences

Valentin · Accepted Answer · 2016-04-04 01:03:46Z

0

In case you are okay with using a data structure from a third party, you may want to use Guava's ArrayListMultimap:

Multimap<Character, Integer> map = ArrayListMultimap.create();
String str = "abcababc";

for (int i = 0 ; i < str.length() ; i++) {
    map.put(str.charAt(i), i);
}

for (Character c : map.keySet()) {
    System.out.println(String.format(%c = %d", c, map.get(c).size());
}

answered Apr 4, 2016 at 1:03

Valentin

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