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Check Index Argument

Source: R/arg_index.R
arg_index.Rd

Checks whether an argument is a valid column index (arg_index()) of a data set or a vector thereof (arg_indices()).

Usage

arg_index(
  x,
  data,
  .arg = rlang::caller_arg(x),
  .arg_data = rlang::caller_arg(data),
  .msg = NULL,
  .call
)

arg_indices(
  x,
  data,
  .arg = rlang::caller_arg(x),
  .arg_data = rlang::caller_arg(data),
  .msg = NULL,
  .call
)

Arguments

x

the argument to be checked

data

a data set (i.e., a matrix or data frame)

.arg

the name of the argument supplied to x to appear in error messages. The default is to extract the argument's name using rlang::caller_arg(). Ignored if .msg is supplied.

.arg_data

the name of the argument supplied to data to appear in error messages. The default is to extract the argument's name using rlang::caller_arg(). Ignored if .msg is supplied.

.msg

an optional alternative message to display if an error is thrown instead of the default message.

.call

the execution environment of a currently running function, e.g. .call = rlang::current_env(). The corresponding function call is retrieved and mentioned in error messages as the source of the error. Passed to err(). Set to NULL to omit call information. The default is to search along the call stack for the first user-facing function in another package, if any.

Value

Returns NULL invisibly if an error is not thrown.

Details

For arg_indices(), an error will be thrown unless one of the following are true:

  • x is a vector of counts (see arg_counts()) less than or equal to ncol(data)

  • x is a character vector with values a subset of colnames(data)

For arg_index(), x additionally must have length equal to 1. Passing arg_index() ensures that data[, x] (if data is a matrix) or data[[x]] (if x is a data frame) evaluate correctly.

If data has no column names, an error will be thrown if x is a character vector.

See also

arg_counts(), arg_character()

Examples

dat <- data.frame(col1 = 1:5,
                  col2 = 6:10)

f <- function(z) {
  arg_index(z, dat)
}

try(f(1))         # No error
try(f(3))         # Error: not a valid index
#> Error : `z` must be the name or index of a column in `dat`.
try(f("col1"))    # No error
try(f("bad_col")) # Error: not a valid index
#> Error : `z` must be the name or index of a column in `dat`.
try(f(1:2))       # Error: arg_index() requires scalar
#> Error : `z` must be the name or index of a column in `dat`.

mat <- matrix(1:9, ncol = 3)

g <- function(z) {
  arg_indices(z, mat)
}

try(g(1))     # No error
try(g(1:3))   # No error
try(g("col")) # Error: `mat` has no names
#> Error : `z` must be the index of a column in `mat`.