Divide based on if else condition

Hi, 

I am trying to do some division based on a filter. I need to create a column called average position which is equal to total position/impressions only when my type is search. Type can have two values search and shopping. I used following formula: 

avg pos = calculate(divide(total pos,impressions,0),type="Search") 

 I am getting desire results when I filter my matrix for search but when I filter for shopping. I can see the values same as search. But I want when I filter data for shopping, avg pos will show 0 or -.

Kindly help

Regards,

Shruti