Word frequency — count occurrences of each word

word_frequency.cell

// ============================================================================
// Word frequency — count occurrences of each word
// ============================================================================
//
// Splits a sentence into words and tallies each into a Map using a list-of
// words walk. Demonstrates building a frequency Map with get-or-default and
// in-place map writes.
//
// Run: soma run word_frequency.cell --signal frequency "the cat the dog the"

cell WordFrequency {
    face {
        signal frequency(text: String) -> Map<String, Int>
        signal most_common(text: String) -> String
    }

    on frequency(text: String) {
        let words = split(lowercase(text), " ")
        let counts = map()
        for w in words {
            if len(w) > 0 {
                let cur = counts[w] ?? 0
                counts[w] = cur + 1
            }
        }
        return counts
    }

    // Return the word with the highest count (first wins on a tie).
    on most_common(text: String) {
        let counts = frequency(text)
        let best = ""
        let best_n = 0
        for w in counts.keys() {
            let n = counts[w]
            if n > best_n {
                best_n = n
                best = w
            }
        }
        return best
    }
}

cell test WordFrequencyTest {
    rules {
        assert frequency("the cat the dog the")["the"] == 3
        assert frequency("the cat the dog the")["cat"] == 1
        assert most_common("a a a b b c") == "a"
        assert most_common("hello") == "hello"
        assert frequency("One ONE one")["one"] == 3
    }
}