MATLAB: Calculating discharge over multiple years

discharge

Need a function that finds the monthly maximum discharge. It should output two values, the discharge itself and the row in which each value occurs. The code should extract results for all months in all years.

I have a data set that has discharge in first column, day, month then year in 2,3 and 4 columns.

Best Answer

Use a table or timetable and rowfun with grouping variables...a couple lines of code and an anonymous function will do it.

For the second desired output you may find augmenting the table with the row number may be the expeditious solution.

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MATLAB: Calculating Discharge Over Multiple Years

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

Best Answer

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