V08 Read an Excel source

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

Optional deep dive. Enable only the options named in each block, after preparing its packages or services.

V08a Read a CSV source

Goal: Separate file reading from definition.

Prerequisites: H04; extras.

Create a small reproducible CSV. The source reads it when executed.

training_step(
  "V08a",
  {
    csv_path <- file.path(training_root, "policies.csv")
    utils::write.csv(policies, csv_path, row.names = FALSE)
    csv_source <- dr_source_file("policies.file", csv_path)
    csv_product <- dr_product(
      "policies.csv",
      csv_source,
      contract = policy_contract
    )
    print(dr_collect(dr_run(csv_product, write = FALSE)))
  },
  needs = c("H04"),
  enabled = training_options$extras,
  optional = TRUE
)

Expected result: Six rows read from a file.

Task: What if the file changes between definition and execution?

V08 Read an Excel source

Goal: Use an appropriate reader.

Prerequisites: H04; readxl, writexl; extras.

writexl only creates the fixture. DataRaft reads Excel through readxl.

training_step(
  "V08",
  {
    xlsx_path <- file.path(training_root, "policies.xlsx")
    writexl::write_xlsx(policies, xlsx_path)
    xlsx_source <- dr_source_file(
      "policies.excel",
      xlsx_path,
      reader = readxl::read_excel
    )
    xlsx_product <- dr_product("policies.excel", xlsx_source) |>
      dr_add_recipe(
        dr_recipe() |> dr_step_mutate(policy_id = as.integer(policy_id))
      ) |>
      dr_add_contract(policy_contract)
    print(dr_collect(dr_run(xlsx_product, write = FALSE)))
  },
  needs = c("H04"),
  packages = c("readxl", "writexl"),
  enabled = training_options$extras,
  optional = TRUE
)

Expected result: Policy IDs are explicitly converted to integer.

Task: Why is this conversion needed?