MATLAB: Remove selected months and years

datevecfindindexnot

Hi,

I am trying to create a matrix where I have removed selected months and years. Here is what I have so far:

dv=datevec(date); %where dv(:,1)=year, dv(:,2)=month and dv(:,3)=day

How do I remove summer of 2009 (i.e., dv(:,1)=2009, dv(:,2)=7 and dv(:,2)=8) and create a new dv?

Thanks!

Best Answer

idx = dv(:,1) == 2019 & ismember(dv(:,2),[6,7,8]); 
dv2 = dv(~idx,:); % to create a new dv
dv(idx,:) = [];   % to remove from existing dv

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MATLAB: Seasonal average over years

Try this demo:

% Make sample data
temps = randi(100, 84, 1)
% Reshape to a month by year array.

tempsByMonth = reshape(temps, 12,7)
% Extract the May - October months.
mayThroughOct = tempsByMonth(5:10,:)
% Get the means over all those extracted months.
meanMayOct = mean(mayThroughOct(:))

Of course it could be make into a more cryptic, obtuse one liner if you wanted, but I went for understandability.

If you have the Image Processing Toolbox, you have mean2() so it can be shortened to

tempsByMonth = reshape(temps, 12,7) % Reshape to a month by year array.
meanMayOct = mean2(tempsByMonth(5:10,:)) % Get the means over extracted months.

and still be fairly readable.

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

Related Solutions

MATLAB: Seasonal average over years

MATLAB: Calculating Discharge Over Multiple Years

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