Indexing by year from full date

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TinaMarie Haskell 2020-11-18

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https://ww2.mathworks.cn/matlabcentral/answers/652608-indexing-by-year-from-full-date

评论： Steven Lord 2020-11-18

I'm working with a data set that provides the date in two ways, yyyymmdd (bot_date) and decimal years (bot_decy). I need to be able to index the data by year (and month) but I'm having trouble separating the dates into year, month, and day.

[bot_yr bot_mon bot_day bot_hr bot_min bot_sec]=datevec(bot_decy);
bot_V=datevec(bot_decy);
 
%ConvertSerialYearToDate(bot_decy);
%[bot_yr bot_mon bot_day bot_hr bot_min bot_sec]=datevec(bot_decy);
%bot_V=datevec(bot_decy);
%BD=datevec(bot_decy);
function [num] = ConvertSerialYearToDate( y )
  year = floor(y);
  partialYear = mod(y,1);
  date0 = datenum(num2str(year),'yyyy');
  date1 = datenum(num2str(year+1),'yyyy');
  daysInYear = date1 - date0;
  num = date0 + partialYear .* daysInYear;
end

These three ways have given me an table like this.

[bot_yr bot_mon bot_day]=datevec(bot_date);
bot_V=datevec(bot_date);
datevec(bot_yr);

This way gives me a weird number for the year (54432 instead of 1988). I've tried it several different ways and I keep getting stuck at these two ends, the table and the weird year.

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Answer 1

Cris LaPierre 2020-11-18

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I'd convert your dates to datetimes. Then you can just use the year, month, and day functions.

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Steven Lord 2020-11-18

在 MATLAB Online 中打开

There's also the ymd function that returns those three quantities in one function call.

But if you have time- and date-based data I'd consider storing it in a timetable array. If you do, using retime to aggregate data based on the date and/or time or using a timerange to index into it could be useful.

MeasurementTime = datetime({'2015-12-18 08:03:05'; ...

'2015-12-18 10:03:17'; ...

'2015-12-18 12:03:13'});

Temp = [37.3;39.1;42.3];

Pressure = [30.1;30.03;29.9];

WindSpeed = [13.4;6.5;7.3];

WindDirection = categorical({'NW';'N';'NW'});

TT = timetable(MeasurementTime,Temp,Pressure,WindSpeed,WindDirection)

TT = 3x4 timetable

MeasurementTime Temp Pressure WindSpeed WindDirection ____________________ ____ ________ _________ _____________ 18-Dec-2015 08:03:05 37.3 30.1 13.4 NW 18-Dec-2015 10:03:17 39.1 30.03 6.5 N 18-Dec-2015 12:03:13 42.3 29.9 7.3 NW

ten = datetime(2015, 12, 18, 10, 0, 0);

tenToEleven = timerange(ten, ten + hours(1))

tenToEleven =

timetable timerange subscript: Select timetable rows with times in the half-open interval: [18-Dec-2015 10:00:00, 18-Dec-2015 11:00:00) See Select Timetable Data by Row Time and Variable Type.

TT(tenToEleven, :)

ans = 1x4 timetable

MeasurementTime Temp Pressure WindSpeed WindDirection ____________________ ____ ________ _________ _____________ 18-Dec-2015 10:03:17 39.1 30.03 6.5 N

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