2.3 Tidy Eval

2.3.1 Pass the dots

No files to be templated in.

Tasks

1. exercise:
   • R/get-matches.R:
     • add ... to formals of uss_get_matches()
     • use ... in dplyr::filter() for results
     • add to documentation (#' @inheritParams dplyr::filter)
     • add to description in documentation
     • add example
   • tests/testthat/test-get-matches.R:
     • test ... works using dplyr::filter()

Result

• we can pass dplyr::filter() expressions to uss_get_matches(), it will filter the results.
• R CMD CHECK will be happy.

2.3.2 Use the pronouns

Template in files:

• R/teams-matches.R
• tests/testthat/test-teams-matches.R

Tasks

1. walk through code, tests
2. usethis::use_import_from("rlang", ".env")
3. in make_teams_matches():

at_home <- FALSE
teams_matches_visitor <-
  data_matches |>
  dplyr::rename(
    team = "visitor",
    opponent = "home",
    goals_against = "goals_home",
    goals_for = "goals_visitor"
  ) |>
  dplyr::mutate(at_home = .env$at_home)

Result

• we have some contrived code
• R CMD CHECK will be happy.

2.3.3 Splice !!!

No files to be templated in.

Tasks

1. in make_teams_matches():

# do this also with teams_matches_home
teams_matches_visitor <-
  data_matches |>
  dplyr::rename(!!!rename_visitor()) |>
  dplyr::mutate(at_home = .env$at_home)

Result

• we have cleaner code
• R CMD CHECK will be happy.

2.3.4 Naming new columns

No files to be templated in.

Tasks

1. usethis::use_import_from("rlang", ":=")
2. in make_teams_matches():

name_of_at_home <- "at_home"
at_home <- FALSE
teams_matches_visitor <-
  data_matches |>
  dplyr::rename(!!!rename_visitor()) |>
  dplyr::mutate("{name_of_at_home}" := .env$at_home)

Result

• we have some very contrived code
• R CMD CHECK will be happy.

2.3.5 across()

No files to be templated in.

Tasks

In make_teams_matches():

1. discuss use of dplyr::select() and dplyr::all_of()
2. add dplyr::arrange() step
3. rerun tests
4. accept change in snapshot

result <-
  teams_matches_home |>
  dplyr::bind_rows(teams_matches_visitor) |>
  dplyr::select(dplyr::all_of(cols_teams_matches())) |>
  dplyr::arrange(
    dplyr::across(
      dplyr::all_of(
        c("country", "tier", "season", "team", "date")
      )
    )
  )

Result

• We get
• R CMD CHECK will be happy.

2.3.6 Exercise

Template in files:

• R/points.R
• R/seasons.R
• tests/testthat/test-points.R
• tests/testthat/test-seasons.R

Tasks

1. walk through code, emphasizing use of function as an argument
2. add new function, uss_make_seasons_final():

• add minimal roxygen at top
• change mutate() to summarise()
• add treatment for date
• change cumsum() to sum()

Result

• we have three new exported functions: uss_points(), uss_make_seasons_cumulative(), uss_make_seasons_final()
• R CMD CHECK will be happy.

2.3.7 Curly-Curly

Template in files:

• R/plot.R
• R/snapshot.R
• tests/testthat/test-plot.R

Tasks

1. usethis::use_package("ggplot2")
2. Walk through code, esp. snapshot code.
3. Add argument aes_y = .data$wins to uss_plot_seasons_tiers(), use {{}} to handle.
4. Add documentation #' @param aes_y ..., example.
5. Uncomment tests.
6. time permitting
   1. change one of the colors ever-so-slightly
   2. run the snapshot tests

Result

• we can use an expression to specify the y-aesthetic
• R CMD CHECK will be happy.