So, you received the result object. This means that the type of the column is non-numerical, but to calculate necessary values, the column need to be numerical. Let's change that.

1. Firstly, we need to replace - with .. To do so, you will apply the method .str.replace() to replace the character in the string in the dataset column. The syntax is
   data['column_name'].str.replace('old_symbol','new_symbol')
   In our case, old_symbol is -, and . is the new_symbol;
2. Then, convert the column to the float data type. To do so, use .astype() method. The syntax is data['column_name'].astype('type').
   In our case, the type is 'float'.