Function pre_eval_transform 

fn pre_eval_transform(
    args: &[Arg],
    env: &Environment,
    context: &BuiltinContext<'_>,
) -> Result<RValue, RError>

Add or modify columns in a data frame.

Evaluates each named ... argument as an expression in the data frame’s column context, adding or replacing columns with the result.

@param _data a data frame @param … named expressions to evaluate (column_name = expression) @return data frame with modified/added columns