H11 Select columns

Use your current course session. Preparation and course runner · R script ↓

H11 Select columns

Goal: Deliberately narrow the output.

Prerequisites: H10.

A strict contract must match the output. Create a separate two-column product rather than silently violating the original contract.

training_step(
  "H11",
  {
    small_recipe <- dr_recipe() |> dr_step_select(policy_id, premium)
    small_contract <- dr_contract(
      "policy.amounts",
      c(policy_id = "integer", premium = "numeric"),
      key = "policy_id"
    )
    small_product <- dr_product(
      "policy.amounts",
      policies,
      contract = small_contract
    ) |>
      dr_add_recipe(small_recipe)
    small_rows <- dr_collect(dr_run(small_product, write = FALSE))
    print(small_rows)
    stopifnot(identical(names(small_rows), c("policy_id", "premium")))
  },
  needs = c("H10")
)

Expected result: Six rows and two columns.

Task: What would happen with the original three-column contract?