Unneeded concatenation linter

Check that the c() function is not used without arguments nor with a single constant.

Usage

unnecessary_concatenation_linter(allow_single_expression = TRUE)

Arguments

allow_single_expression

Logical, default TRUE. If FALSE, one-expression usages of c() are always linted, e.g. c(x) and c(matrix(...)). In some such cases, c() is being used for its side-effect of stripping non-name attributes; it is usually preferable to use the more readable as.vector() instead. as.vector() is not always preferable, for example with environments (especially, R6 objects), in which case list() is the better alternative.

See also

linters for a complete list of linters available in lintr.

Tags

configurable, efficiency, readability, style

Examples

# will produce lints
lint(
  text = "x <- c()",
  linters = unnecessary_concatenation_linter()
)
#> <text>:1:6: style: [unnecessary_concatenation_linter] Replace unnecessary c() by NULL or, whenever possible, vector() seeded with the correct type and/or length.
#> x <- c()
#>      ^~~

lint(
  text = "x <- c(TRUE)",
  linters = unnecessary_concatenation_linter()
)
#> <text>:1:6: style: [unnecessary_concatenation_linter] Remove unnecessary c() of a constant.
#> x <- c(TRUE)
#>      ^~~~~~~

lint(
  text = "x <- c(1.5 + 2.5)",
  linters = unnecessary_concatenation_linter(allow_single_expression = FALSE)
)
#> <text>:1:6: style: [unnecessary_concatenation_linter] Remove unnecessary c() of a constant expression. Replace with as.vector() if c() is used to strip attributes, e.g. in converting an array to a vector.
#> x <- c(1.5 + 2.5)
#>      ^~~~~~~~~~~~

# okay
lint(
  text = "x <- NULL",
  linters = unnecessary_concatenation_linter()
)
#> ℹ No lints found.

# In case the intent here was to seed a vector of known size
lint(
  text = "x <- integer(4L)",
  linters = unnecessary_concatenation_linter()
)
#> ℹ No lints found.

lint(
  text = "x <- TRUE",
  linters = unnecessary_concatenation_linter()
)
#> ℹ No lints found.

lint(
  text = "x <- c(1.5 + 2.5)",
  linters = unnecessary_concatenation_linter(allow_single_expression = TRUE)
)
#> ℹ No lints found.