How to average monthly data using a specific method in Matlab?

I have the following vector of monthly values (vectorA). I put the date related info next to it to help illustrate the task but I work with just the vector itself

dates         month_in_q   vectorA          
31/01/2020       1           10          
29/02/2020       2           15            
31/03/2020       3           6 
30/04/2020       1           8
31/05/2020       2           4
30/06/2020       3           3
vectorA = [10;15;6;8;4;3]

How can I create a new vectorNEW according to this algorithm

• In each quarter the first month is the original first month
• In each quarter the second month is the average of first and second month
• In each quarter the third month is the average of all three months

So that I get the following vectorNEW by manipulating the original vectorA in a loop given this the re-occuring pattern above

vectorNEW = [10;12.5;10.3;8;6;5]
dates         month_in_q   vectorA   vectorNEW       
31/01/2020       1           10          10
29/02/2020       2           15          AVG(10+15)  
31/03/2020       3           6           AVG(10+15+6)
30/04/2020       1           8           8
31/05/2020       2           4           AVG(8+4)
30/06/2020       3           3           AVG(8+4+3)
...              ...        ...          ...   

Answer 1

[dpb]

There may be a more clever way, but brute force seems straightforward enough...

A=reshape(vectorA,3,[]);                                    % temporary to get 3-row array
mnV=reshape([A(1,:); mean(A(1:2,:)); mean(A(1:3,:))],[],1); % build desired means, turn to column vector
clear A                                                     % remove temporary array

AHA! The "more better" way just dawned...knew had to be a cumsum in here somewhere...

mnV=reshape(cumsum(reshape(vectorA,3,[]))./[1:3].',[],1);

[Reginald Pofter]

Thank you, you're spot on. I'll also credit you on stackoverflow with a link to your answer here. I asked the same question there as well.