How to produce a matrix that averages the top 5 values, for a corresponding year?

I would like to produce an average of the top 5 values (on the 5th column, blue) for the corresponding year. I have attached my initial data as an attachment. My difficulty is that the matrix has multiple columns, so how do I choose that column (circled in blue), to calculate averages?

Answer 1

[KSSV]

Let A be your data of dimensions n*4. A has n number of rows and four columns. YOu can extract fourth column from A using.

flows = A(:,4) ;   % This gives you fourth column 
years = A(:,1) ;   % This extracts the years from the data 
% GEt mean of top five elements 
iwant = mean(flows(1:5)) ;

If you have multiple years in the data, then you need to extract the respective year flows and get mean of top five values.

flows_1938 = flows(years==1938) ;    % This gives flows of the year 1938
iwant_1938 = mean(flows(1:5)) ;

[Naveed Hossain]

Would you happen to know how to produce a matrix, where it would look like the following:

Year Flows
1938 (Top 5 Average for 1938)
1939  (Top 5 average for 1939)
1940            etc
 end

[KSSV]

flows = A(:,4) ;   % This gives you fourth column 
years = A(:,1) ;   % This extracts the years from the data 
% GEt years alone 
[Y,ia,ib] = unique(years) ;
NY = length(Y) ;    % number of years 
iwant = zeros(N,2) ;
for i =1:n
    F = flows(years==Y(i)) ;
    if length(F)>5
        iwant(i,:) = [Y(i) mean(F(1:5))] ;
    else
        iwant(i,:) = [Y(i) mean(F)] ;
    end
end