Joining Datasets

033_join_data.cell

// ============================================================================
// 033 — Joining Datasets
// ============================================================================
// join() and left_join() combine two lists on a shared key.
//
// Run:   soma run 033_join_data.cell run
// Expect:
//   Inner join (only matches):
//     Alice: Eng
//     Carol: Sales
//   Left join (keep all from left):
//     Alice: Eng
//     Bob: (no department)
//     Carol: Sales

cell JoinData {

    on run() {
        // Two separate datasets with a shared "id" field
        let employees = list(
            map("id", 1, "name", "Alice"),
            map("id", 2, "name", "Bob"),
            map("id", 3, "name", "Carol")
        )

        let departments = list(
            map("id", 1, "dept", "Eng"),
            map("id", 3, "dept", "Sales")
        )

        // join() — inner join: only rows that exist in both lists
        let inner = join(employees, departments, "id")
        print("Inner join (only matches):")
        for row in inner {
            print("  {row.name}: {row.dept}")
        }

        // left_join() — keeps all rows from the left list
        let left = left_join(employees, departments, "id")
        print("Left join (keep all from left):")
        for row in left {
            let dept = row.dept ?? "(no department)"
            print("  {row.name}: {dept}")
        }

        return "done"
    }
}