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()
)
#> ::warning file=<text>,line=1,col=6::file=<text>,line=1,col=6,[unnecessary_concatenation_linter] Unneeded concatenation without arguments. Replace the "c" call by NULL or, whenever possible, vector() seeded with the correct type and/or length.

lint(
  text = "x <- c(TRUE)",
  linters = unnecessary_concatenation_linter()
)
#> ::warning file=<text>,line=1,col=6::file=<text>,line=1,col=6,[unnecessary_concatenation_linter] Unneeded concatenation of a constant. Remove the "c" call.

lint(
  text = "x <- c(1.5 + 2.5)",
  linters = unnecessary_concatenation_linter(allow_single_expression = FALSE)
)
#> ::warning file=<text>,line=1,col=6::file=<text>,line=1,col=6,[unnecessary_concatenation_linter] Unneeded concatenation of a simple expression. Remove the "c" call, replacing with "as.vector" if using "c" to string attributes, e.g. in converting an array to a vector.

# okay
lint(
  text = "x <- NULL",
  linters = unnecessary_concatenation_linter()
)

# In case the intent here was to seed a vector of known size
lint(
  text = "x <- integer(4L)",
  linters = unnecessary_concatenation_linter()
)

lint(
  text = "x <- TRUE",
  linters = unnecessary_concatenation_linter()
)

lint(
  text = "x <- c(1.5 + 2.5)",
  linters = unnecessary_concatenation_linter(allow_single_expression = TRUE)
)