Isn’t the issue here the difference between symbol_list and symbol_list2?
The errors just tell you the length is not defined for DataFrames (you would want nrow in that case).
symbol_list in your code is a DataFrame, while symbol_list.Symbol is a vector (for which length is defined). You’re not showing how symbol_list2 is defined, but it appears to be a vector as well (maybe you did symbol_list2 = symbol_list.Symbol somehwere?)