Block usage of pipeline placeholders if unnecessary

The argument placeholder . in magrittr pipelines is unnecessary if passed as the first positional argument; using it can cause confusion and impacts readability.

Usage

unnecessary_placeholder_linter()

Details

This is true for forward (%>%), assignment (%<>%), and tee (%T>%) operators.

See also

linters for a complete list of linters available in lintr.

Tags

best_practices, readability

Examples

# will produce lints
lint(
  text = "x %>% sum(., na.rm = TRUE)",
  linters = unnecessary_placeholder_linter()
)
#> <text>:1:11: warning: [unnecessary_placeholder_linter] Don't use the placeholder (`.`) when it's not needed, i.e., when it's only used as the first positional argument in a pipeline step.
#> x %>% sum(., na.rm = TRUE)
#>           ^

# okay
lint(
  text = "x %>% sum(na.rm = TRUE)",
  linters = unnecessary_placeholder_linter()
)
#> ℹ No lints found.

lint(
  text = "x %>% lm(data = ., y ~ z)",
  linters = unnecessary_placeholder_linter()
)
#> ℹ No lints found.

lint(
  text = "x %>% outer(., .)",
  linters = unnecessary_placeholder_linter()
)
#> ℹ No lints found.