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Date to Decimal Day of Year

Date to Decimal Day of Year

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14 Jan 2008 (Updated )

Convert a vector of MATLAB serial dates to decimal days since the start of the year.

date2doy(inputDate)
function [doy,fraction] = date2doy(inputDate)
%DATE2DOY  Converts the date to decimal day of the year.
%   [doy,fraction] = date2doy(inputDate)
%
%   Descriptions of Input Variables:
%   inputDate:  Input date as a MATLAB serial datenumber
%
%   Descriptions of Output Variables:
%   doy: Decimal day of the year. For instance, an output of 1.5 would 
%       indicate that the time is noon on January 1.
%   fraction: Outputs the fraction of a year that has elapsed by the input
%       date.
%
%   Example(s):
%   >> [doy,frac] = date2doy(datenum('1/25/2004'));
%
%   See also:

% Author: Anthony Kendall
% Contact: anthony [dot] kendall [at] gmail [dot] com
% Created: 2008-03-11
% Copyright 2008 Michigan State University.

%Want inputs in rowwise format
[doy,fraction] = deal(zeros(size(inputDate)));
inputDate = inputDate(:);

%Parse the inputDate
[dateVector] = datevec(inputDate);

%Set everything in the date vector to 0 except for the year
dateVector(:,2:end) = 0;
dateYearBegin = datenum(dateVector);

%Calculate the day of the year
doyRow = inputDate - dateYearBegin;

%Optionally, calculate the fraction of the year that has elapsed
flagFrac = (nargout==2);
if flagFrac
    %Set the date as the end of the year
    dateVector(:,1) = dateVector(:,1) + 1;
    dateYearEnd = datenum(dateVector);
    fracRow = (doyRow - 1) ./ (dateYearEnd - dateYearBegin);
end

%Fill appropriately-sized output array
doy(:) = doyRow;
if flagFrac
    fraction(:) = fracRow;
end

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