How is "quartely" defined in the function retime?

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Fabrice Lambert 2020-5-29

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https://ww2.mathworks.cn/matlabcentral/answers/537099-how-is-quartely-defined-in-the-function-retime

评论： Fabrice Lambert 2020-5-30

采纳的回答： Adam Danz

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Hi. I am using retime to get quarterly mean data from irregularly distributed measurements:

yTT = retime(xTT,'quarterly',@nanmean);

My first measurement is on the 1st of April. The new yTT timetable has now timesteps at April, July, September, and January. My question is now are these quarterly values means of the widely used Mar-Apr-May, Jun-Jul-Aug, Sep-Oct-Nov, and Dec-Jan-Feb? Or is the April quarterly value an average of Apr-May-Jun, and so on?

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Answer 1

Adam Danz 2020-5-29

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According to Wiki,

In Gregorian calendar:

First quarter, Q1: 1 January – 31 March (90 days or 91 days in leap years)
Second quarter, Q2: 1 April – 30 June (91 days)
Third quarter, Q3: 1 July – 30 September (92 days)
Fourth quarter, Q4: 1 October – 31 December (92 days)

While in the Chinese calendar, the quarters are traditionally associated with the 4 seasons of the year:

Spring: 1st to 3rd month
Summer: 4th to 6th month
Autumn: 7th to 9th month
Winter: 10th to 12th month

https://en.wikipedia.org/wiki/Calendar_year

The months you see are the first month within the quarter.

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Adam Danz 2020-5-30

编辑：Adam Danz 2020-5-30

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Thanks for the comment, Fabrice Lambert. Where in the synchronize function did you see that (using r2020a, I assume)?

This example suggests otherwise. The timetable starts on Feb-1-2019 and contains a value for every 3 months but some of the 3-month periods are missing. When the retime fills in the table using the quarterly times, the output timetable only shows the starting month of each gregorian quarter.

startdate = datetime(2019,02,01); 
dates = startdate + calmonths(0:3:30)'; 
dates([2,5,10]) = []; 
TT = timetable(dates, (1:numel(dates))'); % Input
TTr = retime(TT,'quarterly','previous');  % Output retime'd
% TT =
%   8×1 timetable
%        dates       Var1
%     ___________    ____
%     01-Feb-2019     1  
%     01-Aug-2019     2  
%     01-Nov-2019     3  
%     01-May-2020     4  
%     01-Aug-2020     5  
%     01-Nov-2020     6  
%     01-Feb-2021     7  
%     01-Aug-2021     8  
% TTr =
%   12×1 timetable
%        dates       Var1
%     ___________    ____
%     01-Jan-2019    NaN 
%     01-Apr-2019      1 
%     01-Jul-2019      1 
%     01-Oct-2019      2 
%     01-Jan-2020      3 
%     01-Apr-2020      3 
%     01-Jul-2020      4 
%     01-Oct-2020      5 
%     01-Jan-2021      6 
%     01-Apr-2021      7 
%     01-Jul-2021      7 
%     01-Oct-2021      8 

Adam Danz 2020-5-30

编辑：Adam Danz 2020-5-30

You're exactly right. That section of the code shifts the starting time of the timetable to the nearest quarter and then increments by 3-months from there.

I also agree that the documentation could be clearer. If you go to the retime() and synchronize() documentation pages online and scroll to the bottom, you can give those pages a star rating and then a window will appear allowing you to give feedback. I'll make this suggestion on both pages (you could, too, if you'd like).

Fabrice Lambert 2020-5-30