Indexing by year from full date

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.

Answer 1

[Cris LaPierre]

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

[Steven Lord]

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