Assert input is a scalar — assert

Assert that an object is a scalar, meaning it is a length 1 atomic vector (such as numeric(1), character(1) or logical(1)). Note lists, data.frames and matrices are never considered scalar objects, even if they have only one element.

Usage

assert_scalar(x, msg = NULL, call = rlang::caller_env(), arg_name = NULL)

Arguments

x: An object
msg: A character string containing the error message to display if x is not a scalar
call: Only relevant when pooling assertions into multi-assertion helper functions. See cli_abort for details.
arg_name: Advanced use only. Name of the argument passed (default: NULL, will automatically extract arg_name).

Value

invisible(TRUE) if x is a scalar, otherwise aborts with the error message specified by msg

Examples


# Pass when value is scalar
assert_scalar(5) # Passes
assert_scalar("single string") # Passes
assert_scalar(TRUE) # Passes

# Fail when value is not
try({
assert_scalar(c(1, 2, 3)) # Throws default error
assert_scalar(matrix(1:4, 2, 2)) # Throws default error
})
#> Error in eval(expr, envir) : 
#>   'c(1, 2, 3)' must be a scalar, not a numeric