Quickstart - Word Count Single-Threaded Computation

We want to count how many times each word occurs in the text. If we want to do a word count without using a DAG and in a single-threaded computation, we could do it as shown below:

Pattern pattern = Pattern.compile("\\s+");
Map<String, Long> counts = new HashMap<>();
for (String line : map.values()) {
    for (String word : pattern.split(line)) {
        counts.compute(word.toLowerCase(), (w, c) -> c == null ? 1L : c + 1);
    }
}

As soon as we try to parallelize this computation, it becomes clear that we have to model it differently. More complications arise on top of that when we want to scale out across multiple machines.