Calculate Mean of Ratios

Question

I have dataset such as:

Person  Code  Value       
1         A     5      
1         B     6     
1         C     7     
2         A     10    
2         B     11    
2         C     12     
3         A     10    
4         B     8     

The way to interpret the data is that person 1 performed code A for 5 times and code B for 6 times. I am interested to find the ratio of code A/code B. There are missing codes for certain people, such as person 4 does not have code A. For missing values, I replace with 0, since person 4 does not perform code A. I calculate the ratio A/B for everyone such that:

Person  RatioAB        
1         5/6
2         10/11
3         Inf
4         0

My goal is to find the average ratio A/B for all 4 people.

What is the correct way to do this in statistical study?

1. Should I only consider person 1,2 and 4 and their mean ratio which is 0.58?
2. Should I first remove any person without both A and B (person 3 and person 4), and only calculate the average ratio based on person 1 and 2?
3. Average of A/Average of B

My actual dataset consists of millions of people.