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Identify cases where stringsAsFactors should be supplied explicitly

Source: R/strings_as_factors_linter.R
strings_as_factors_linter.Rd

Designed for code bases written for versions of R before 4.0 seeking to upgrade to R >= 4.0, where one of the biggest pain points will surely be the flipping of the default value of stringsAsFactors from TRUE to FALSE.

Usage

strings_as_factors_linter()

Details

It's not always possible to tell statically whether the change will break existing code because R is dynamically typed -- e.g. in data.frame(x) if x is a string, this code will be affected, but if x is a number, this code will be unaffected. However, in data.frame(x = "a"), the output will unambiguously be affected. We can instead supply stringsAsFactors = TRUE, which will make this code backwards-compatible.

See https://developer.r-project.org/Blog/public/2020/02/16/stringsasfactors/.

See also

linters for a complete list of linters available in lintr.

Tags

robustness

Examples

# will produce lints
lint(
  text = 'data.frame(x = "a")',
  linters = strings_as_factors_linter()
)
#> ::warning file=<text>,line=1,col=1::file=<text>,line=1,col=1,[strings_as_factors_linter] This code relies on the default value of stringsAsFactors, which changed in version R 4.0. Please supply an explicit value for stringsAsFactors for this code to work with versions of R both before and after this switch.

# okay
lint(
  text = 'data.frame(x = "a", stringsAsFactors = TRUE)',
  linters = strings_as_factors_linter()
)

lint(
  text = 'data.frame(x = "a", stringsAsFactors = FALSE)',
  linters = strings_as_factors_linter()
)

lint(
  text = "data.frame(x = 1.2)",
  linters = strings_as_factors_linter()
)