CSV split/join — parse rows and project columns

csv.cell

// ============================================================================
// CSV split/join — parse rows and project columns
// ============================================================================
//
// Splits a CSV body into rows (by newline) and each row into fields (by comma),
// then maps header names to a list of record Maps. Demonstrates split on "\n"
// and ",", zipping headers to values, and join to re-serialize a row.
//
// Run: soma run csv.cell --signal parse "name,age\nAlice,30\nBob,25"

cell Csv {
    face {
        signal parse(body: String) -> List<Map>
        signal row_to_line(row: List<String>) -> String
        signal column(body: String, field: String) -> List<String>
    }

    on parse(body: String) {
        let lines = split(body, "\n") |> filter(l => len(l) > 0)
        if len(lines) == 0 { return list() }
        let headers = split(lines[0], ",")
        let rows = list()
        for r in range(1, len(lines)) {
            let cells = split(lines[r], ",")
            let rec = map()
            for c in range(0, len(headers)) {
                rec[headers[c]] = cells[c]
            }
            rows = push(rows, rec)
        }
        return rows
    }

    on row_to_line(row: List<String>) {
        return join(row, ",")
    }

    // Pull a single column out as a list of strings.
    on column(body: String, field: String) {
        let rows = parse(body)
        return rows |> map(r => r[field])
    }
}

cell test CsvTest {
    rules {
        assert len(parse("name,age\nAlice,30\nBob,25")) == 2
        assert parse("name,age\nAlice,30\nBob,25")[0]["name"] == "Alice"
        assert parse("name,age\nAlice,30\nBob,25")[1]["age"] == "25"
        assert row_to_line(list("a", "b", "c")) == "a,b,c"
        assert column("city\nParis\nRome", "city")[1] == "Rome"
    }
}