Pasting Data in Quarterly Format from Data in Monthly Format

Hello everyone,

I've started to work on some more heavy statistics, where I already have monthly data and am trying to paste it as quarterly data. I have two questions related to this, if I may.

For your reference, I've attached my spreadsheet: US Unemployment Rate.xls

First, from all the monthly data, I would like the desired column (uert) to have only the March, June, Sep, and Dec values (highlighted in yellow), in order by year of course.
In other words, for my first quarter, I just take the value in March. For the second quarter, I just take the value in June.

Second, from all the monthly data, I would like the desired column uertavg to be the averages of every three months, matching each quarter, in order by year.
In other words, for my first quarter, I'd average {Jan, Feb, Mar}. For the second quarter, I'd average {Apr, May, June}.


To illustrate my goal, I've listed the first few values of uert and uertavg by reading the value in my original spreadsheet and typing it manually.

Thank you very much for your help!