Detect a random slope in a model formula

Parses the formula and inspects every grouping term written as (lhs | g) or (lhs || g). A term carries a random slope when its left-hand side names a variable; constant-only sides such as 1, 0 + 1, or the brms ID form (1 | ID | g) do not.

Usage

has_random_slope(formula_str)

Arguments

formula_str

Character formula string.

Value

Logical scalar; FALSE when the string does not parse.

Examples

has_random_slope("outcome ~ level_AB + (1 | case)")
#> [1] FALSE
has_random_slope("outcome ~ level_AB + (0 + level_AB || case)")
#> [1] TRUE