d = (1:36)' ; % let this be number of days
z = rand(size(d)) ; % let this be your water level
% make d divisble by 7 for reshaping
n = length(d) + (7 - rem(length(d),7)) ;
n = n-length(d) ;
d = [d ; NaN(n,1)] ; % append NaN's if extra values are needed
z = [z ; NaN(n,1)] ; % append NaN's if extra values are needed
% reshape to 7 rows
d = reshape(d,7,[]) ;
z = reshape(z,7,[]) ;
iwant = max(z) ; % get maximum for each 7 days
