# Click Through Rate calculation (CTR) calculation problem

So I'm doing a use case for a company interview and one of the questions is to calculate the CTR for a sorting algorithm.

My question would be: Should I remove the operations where there were no products shown (even though some of them there were clicks on products)?Example (should discard this columns?):

Number of impressions | Number of clicks
0         |      1
0         |      3
0         |      0


CTR = #products clicked/#products shown

My other doubt is wether should I sum the clicks and the products shown and then divide one on other OR should I do the CTR for each operation:

Pseudo Python code (imagine that I have a dataframe with several operations as rows):

CTR = pd_df["no_clicks"].sum() / pd_df["no_impressions"].sum()


OR

pd_df["CTR"] = pd_df["no_clicks"] / pd_df["no_impressions"]
CTR = pd_df["CTR"].mean()