Save a number filtered by a dimension in a field to use it for further calculations

[Looker_T]

Hi everyone,

I’m using looker studio for analytics data and have a roadblocker at the moment. In GA there is a dimension called event action with for instance “add to cart”, “view product detail”, “clicked on product” etc. In addition there is a metric called individual actions. For a certain timeframe I can for instance filter to event to “add to cart” and analyse the metric individual actions. Lets say there were 500 individual actions tracked for the “add to cart” event. Now I want to store this 500 hits in another variable. I want to use this variable further to calculate add to cart ratio etc. How can I come up with a calculated field, that will store the information above? 

Thanks looker_T