Check that a model formula uses only data columns and brms term syntax

Formula text typed into the app reaches brms and model.frame(), which evaluate calls such as I(q()). This check accepts data columns, the constants 0 and 1, the operators ~ + : * | || / - (, and the brms helpers ar() (named time, gr, cov arguments), gr(), trials(), and the exposure offset offset(log(<column>)); every other function call, string, $, @, or :: is rejected.

Usage

is_safe_formula(x, allowed_vars)

Arguments

x

Formula string, either a full formula ("y ~ x + (1 | case)") or a right-hand side.

allowed_vars

Column names of the analysis data.

Value

Logical scalar.

Examples

is_safe_formula("y ~ level_AB + (1 | case)", c("y", "level_AB", "case"))
#> [1] TRUE
is_safe_formula("y ~ I(q())", "y")
#> [1] FALSE