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Convert string expression to function

stm_function.Rd

stm_function() converts a function or string representation of an expression into a valid R function. Checks variable compatibility and provides warnings or errors as necessary.

Usage

stm_function(fexpr, vars = NULL, nvars = NULL, par_name = "fexpr")

Arguments

fexpr

A function or string representing a mathematical expression. Strings must represent valid mathematical expressions.

vars

Optional. A character vector of expected variable names. Default is NULL meaning that variables will be assumed for multi-variable expressions.

nvars

Optional. An integer specifying the expected number of variables in the expression. Raises an error if the count differs. Default is NULL

par_name

Optional. A string used in error and warning messages to refer to the parameter. Defaults is "fexpr".

Value

If fexpr is a function, it is returned unchanged. If it is a string, a callable R function is constructed and returned.

Details

The function checks whether fexpr is a valid function or expression. If it is a string, variables are identified and a callable function is constructed. If nvars is specified and does not match the variable count, an error is raised. If vars is not specified and multiple variables are found, a warning is issued and default names are assumed.

See also

stm_function, stm_fexpr_vars

Examples

f <- stm_function(
  fexpr = "2 * x + sqrt(y) + cos(a) / pi", 
  vars = c("x", "y", "a")
)
f(3, 4, 5)
#> [1] 8.090292
f(x = 3, y = 4, a = 5)
#> [1] 8.090292
f(a = 3, x = 4, y = 5)
#> [1] 9.920944