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Block usage of anonymous functions in iteration functions when unnecessary

Source: R/unnecessary_lambda_linter.R
unnecessary_lambda_linter.Rd

Using an anonymous function in, e.g., lapply() is not always necessary, e.g. lapply(DF, sum) is the same as lapply(DF, function(x) sum(x)) and the former is more readable.

Usage

unnecessary_lambda_linter()

Details

Cases like lapply(x, \(xi) grep("ptn", xi)) are excluded because, though the anonymous function can be avoided, doing so is not always more readable.

See also

linters for a complete list of linters available in lintr.

Tags

best_practices, efficiency, readability

Examples

# will produce lints
lint(
  text = "lapply(list(1:3, 2:4), function(xi) sum(xi))",
  linters = unnecessary_lambda_linter()
)
#> ::warning file=<text>,line=1,col=24::file=<text>,line=1,col=24,[unnecessary_lambda_linter] Pass sum directly as a symbol to lapply() instead of wrapping it in an unnecessary anonymous function. For example, prefer lapply(DF, sum) to lapply(DF, function(x) sum(x)).

# okay
lint(
  text = "lapply(list(1:3, 2:4), sum)",
  linters = unnecessary_lambda_linter()
)

lint(
  text = 'lapply(x, function(xi) grep("ptn", xi))',
  linters = unnecessary_lambda_linter()
)

lint(
  text = "lapply(x, function(xi) data.frame(col = xi))",
  linters = unnecessary_lambda_linter()
)