Block usage of anonymous functions in iteration functions when unnecessary

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(allow_comparison = FALSE)

Arguments

allow_comparison

Logical, default FALSE. If TRUE, lambdas like function(x) foo(x) == 2, where foo can be extracted to the "mapping" function and == vectorized instead of called repeatedly, are linted.

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, configurable, efficiency, readability

Examples

# will produce lints
lint(
  text = "lapply(list(1:3, 2:4), function(xi) sum(xi))",
  linters = unnecessary_lambda_linter()
)
#> <text>:1:24: warning: [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)).
#> lapply(list(1:3, 2:4), function(xi) sum(xi))
#>                        ^~~~~~~~~~~~~~~~~~~~

lint(
  text = "sapply(x, function(xi) xi == 2)",
  linters = unnecessary_lambda_linter()
)
#> ℹ No lints found.

lint(
  text = "sapply(x, function(xi) sum(xi) > 0)",
  linters = unnecessary_lambda_linter()
)
#> <text>:1:24: warning: [unnecessary_lambda_linter] Compare to a constant after calling sapply() to get the full benefits of vectorization. Prefer sapply(x, foo) == 2 over sapply(x, function(xi) foo(xi) == 2, logical(1L)).
#> sapply(x, function(xi) sum(xi) > 0)
#>                        ^~~~~~~~~~~

# okay
lint(
  text = "lapply(list(1:3, 2:4), sum)",
  linters = unnecessary_lambda_linter()
)
#> ℹ No lints found.

lint(
  text = 'lapply(x, function(xi) grep("ptn", xi))',
  linters = unnecessary_lambda_linter()
)
#> ℹ No lints found.

lint(
  text = "lapply(x, function(xi) data.frame(col = xi))",
  linters = unnecessary_lambda_linter()
)
#> ℹ No lints found.

lint(
  text = "sapply(x, function(xi) xi == 2)",
  linters = unnecessary_lambda_linter(allow_comparison = TRUE)
)
#> ℹ No lints found.

lint(
  text = "sapply(x, function(xi) sum(xi) > 0)",
  linters = unnecessary_lambda_linter(allow_comparison = TRUE)
)
#> ℹ No lints found.

lint(
  text = "sapply(x, function(xi) sum(abs(xi)) > 10)",
  linters = unnecessary_lambda_linter()
)
#> ℹ No lints found.

lint(
  text = "sapply(x, sum) > 0",
  linters = unnecessary_lambda_linter()
)
#> ℹ No lints found.