Count how many times a word occurs in a HashMap per key

Question

I have a HashMap in which sentence records are stored with an associated key. Now, an output should be created in this displayed how much the word (in my example the word "car") in this index (key) occurs. For example, if the word "car" occurs in the index (key) 5, 4 times, the 5 should also be output 4 times.

The current output is: Car : [1, 2, 3, 5]

My desired output is: Car : [1, 1, 2, 3, 3, 5, 5, 5, 5]

Map<Integer, String> carHashMap = new HashMap<>();
ArrayList<Integer> showCarsInMap = new ArrayList<>();

carHashMap.put(1, "this car is very fast car");
carHashMap.put(2, "i have a old car");
carHashMap.put(3, "my first car was an mercedes and my second car was an audi");
carHashMap.put(4, "today is a good day");
carHashMap.put(5, "car car car car");

for (Map.Entry<Integer, String> entrySection : carHashMap.entrySet()) {

    if (entrySection.getValue().contains("car")) {

        showCarsInMap.add(entrySection.getKey());

    }
}

System.out.println("Car : " + showCarsInMap);

I guess I have to add an additional if-loop, but I don't know how my program can recognize which "car" has already been counted and which not.

`contains` doesn't help when you want to interact with multiple matches. Use the `indexOf` variant with a `fromIndex` parameter in your loop. — Joachim Sauer, Oct 31 '22 at 15:28
What are the rules for partial matches? eG should `"ay caramba"` also count as 1 match for `"car"` or do you only want to count whole word matches? — OH GOD SPIDERS, Oct 31 '22 at 15:31
@OHGODSPIDERS no the word "ay caramba" should not count. Do you have any advice? — OnlyProblems, Oct 31 '22 at 15:42
In that case, since `"ay caramba".contains("car")` returns true and `"ay caramba".indexOf("car")` would return a positive value you couldn't use either of those methods. You could, as a first step [Convert the sentence string to a string array of words in Java](https://stackoverflow.com/questions/4674850/converting-a-sentence-string-to-a-string-array-of-words-in-java), then iterate ofer that array of words and compare it with your target word via `equals` or `equalsIgnoreCase` — OH GOD SPIDERS, Oct 31 '22 at 15:49

score 2 · Accepted Answer · answered Oct 31 '22 at 15:56

I suggest you simply use regex for this:

for (Map.Entry<Integer, String> entrySection : carHashMap.entrySet()) {
     Pattern p = Pattern.compile("(?:^|\\W)car(?:$|\\W)"); //This will only capture the exact word, as dicussed in the comments.
     Matcher m = p.matcher(entrySection.getValue());
     while (m.find()) {
           showCarsInMap.add(entrySection.getKey());
     }
}

Regex is from here.

Ashish Patil · Answer 2 · 2022-10-31T16:33:30.303

Though not ideal but this will work:

carHashMap.entrySet().stream().forEach(x -> {
            long count = Arrays.stream(x.getValue().split(" ")).filter(t -> t.equalsIgnoreCase("car")).count();
            while (count-- > 0) {
                showCarsInMap.add(x.getKey());
            }
        });

Here, I am considering you are only going to have space(" ") as a separator. Also, you don't need to use for loop but you can use streams directly on hashmap.

Count how many times a word occurs in a HashMap per key

2 Answers2