scalar_in_linter: Block usage like x %in% "a"

In lintr: A 'Linter' for R Code

Block usage like x %in% "a"

Description

vector %in% set is appropriate for matching a vector to a set, but if that set has size 1, == is more appropriate. However, if vector has also size 1 and can be NA, the use of == should be accompanied by extra protection for the missing case (for example, isTRUE(NA == "arg") or !is.na(x) && x == "arg").

Usage

scalar_in_linter(in_operators = NULL)

Arguments

in_operators

Character vector of additional infix operators that behave like the %in% operator, e.g. {data.table}'s ⁠%chin%⁠ operator.

Details

scalar %in% vector is OK, because the alternative (any(vector == scalar)) is more circuitous & potentially less clear.

Tags

best_practices, configurable, consistency, efficiency, readability

See Also

linters for a complete list of linters available in lintr.

Examples

# will produce lints
lint(
  text = "x %in% 1L",
  linters = scalar_in_linter()
)

lint(
  text = "x %chin% 'a'",
  linters = scalar_in_linter(in_operators = "%chin%")
)

# okay
lint(
  text = "x %in% 1:10",
  linters = scalar_in_linter()
)

lintr documentation built on Nov. 27, 2025, 9:06 a.m.