Calculating Discharge Over Multiple Years

I have a time series dataset which consists of the year in column 1 from 1883 - 2018, in column 2 there is month data and in column 3 each day. In column 4 there is a discharge value for each specific day. I need to calculate the maximum discharge for each year.

I am new to matlab and any help would be greatly appreciated

Thanks!

Answer 1

[Adam Danz]

The first 3 lines re-create the input matrix named m. See inline comments to understand the rest.

It produces a table T summarizing the results.

% recreate input data (m)
d = datetime(1883,9,1) : days(1) : datetime(1950,12,31);
[yr,mo,dy] = datevec(d); 
m = [yr(:),mo(:),dy(:),rand(size(yr(:)))*50+40];

% Identify winter months 
winterMonths = [11, 12, 1]; % any order but must be consecutive months
isWinter = ismember(m(:,2), winterMonths); 

% group the consecutive winter months
L = bwlabel(isWinter); %requires image processing toolbox

% -------------------------------------------------------
% % If you don't have image processing tool box:          %
% isWinterCS = cumsum(diff([0;isWinter]) == 1);           %
% L = zeros(size(isWinter));                              %
% L(isWinter) = isWinterCS(isWinter);                     %
% -------------------------------------------------------

% Compute max dischage per annual winter
maxDischarge = grpstats(m(:,4),L,'max'); %requires stats & ML toolbox

% Organize data by year (using the earliest year in each winter)
maxDischargeYear = grpstats(m(:,1),L,'min'); %requires stats & ML toolbox

% -------------------------------------------------------
% % If you don't have stats & ML tool box:                %
% groupID = findgroups(L);                                %
% maxDischarge = splitapply(@max,m(:,4),groupID);         %
% maxDischargeYear = splitapply(@min,m(:,1),groupID);     %
% -------------------------------------------------------

maxDischargeYear(1) = []; % Remove group 0 (non-winter months)
maxDischarge(1) = [];     % Remove group 0 (non-winter months)
T = table(maxDischargeYear(:),maxDischarge(:),'VariableNames',{'Year','MaxDischarge'});

% Show first few rows
head(T)

%     Year    MaxDischarge
%     ____    ____________
% 
%     1883       89.476   
%     1884       89.657   
%     1885       89.815   
%     1886       89.866   
%     1887       89.884   
%     1888       88.552   
%     1889       89.299   
%     1890       89.571   

[will]

Thank you Adam this helps alot, however I dont have image processing toolbox how would I do this without using it?

Thanks

[Adam Danz]

I added 3 lines to my solution that you can use if you do not have image processing toolbox. And I added another 3 lines you can use if you don't have Stats & ML Toolbox.

See my updated answer.

[will]

This working perfectly aswell thank you for all of your help!

Answer 2

[Patrick Gipper]

Less elegent and more brute force, but no toolbox required. Not sure what would happen with a missing year or if there happens to be multiple days in a given winter with the same maximum.

[will]

Thank you very much this works perfectly!