So I have some data that has a user, a purchase, and a date. I am hoping to accomplish a couple of things with the data. First, I want to show a line graph plotting the purchase amounts over time, per month and week, by each customer. But I don't care when during the month they occur, as long as they appear in August, I just want to have purchase 1 in August, purchase 2 in August, etc. I want the same thing on a weekly basis. In Excel, I can set up a couple of Countifs formulas and have them give me the counts/indexes. I'd prefer to have the data come in and not have to add anything to it outside of Tableau. So what sort of calculated field would I need to create for that?

My second hope is to be able to look at an expected next purchase. ie, if someone spent $20 previously, they've then spent $30 next twice and $10 once. For the data points of $20, I'd like to include the value of the next purchase. Again, I am able to do this in Excel but would prefer not to have to add anything before looking at it in Tableau.

I've attached a CSV file with all of the fields I use and create. The first three (Date, Customer, Amount) are data I am given, I create Month, Week, Month Purchase, Week Purchase, Lookup, and Next Amount.

Any and all help is greatly appreciated.