/// <summary> /// Coerce the specified expression to an S4 object. /// </summary> /// <param name="expression">The expression.</param> /// <returns>The DataFrame. Returns <c>null</c> if the specified expression is not vector.</returns> public static S4Object AsS4(this SymbolicExpression expression) { if (!expression.IsS4()) { return(null); } return(new S4Object(expression.Engine, expression.DangerousGetHandle())); }