Converting Date Format to serial date

I have a data set ( Sourced originally from NASA, GISS) which includes the date (in what i think is decimal date?!) and the northern hemisphere monthly temperature anomaly. Below is a section of the date:

Date Temp Ann

1880.0000 -0.404500

1880.0834 -0.570571

1880.1666 -0.313143

1880.2500 -0.360071

1880.3334 -0.113643

1880.4166 -0.209643

1880.5000 -0.230857

1880.5834 -0.296357

1880.6666 -0.282214

1880.7500 -0.401439

1880.8334 -0.505396

1880.9166 -0.417626

1881.0000 -0.344500

1881.0834 -0.280571

1881.1666 -0.113143

I need to convert the date into matlab serial date. I've tried datenum which obviously will not work on this format.

In all honesty im not 100% sure what the format actually is.

Any help in recognising the correct format and how to convert it would be greatly appreciated.

Answer 1

[Star Strider]

I’m not certain what the decimals are, however they appear to be sequential so they may be fractions of a year.

Unfortunately datetime isn’t set up for years and fraction-of-years, at least not that I can determine. It would be nice to have that option. (I experimented with the ‘epoch’ options, however they produced reults that were obviously wrong.)

A = [1880.0000   -0.404500    
     1880.0834   -0.570571    
     1880.1666   -0.313143    
     1880.2500   -0.360071    
     1880.3334   -0.113643    
     1880.4166   -0.209643    
     1880.5000   -0.230857    
     1880.5834   -0.296357    
     1880.6666   -0.282214    
     1880.7500   -0.401439    
     1880.8334   -0.505396    
     1880.9166   -0.417626    
     1881.0000   -0.344500    
     1881.0834   -0.280571    
     1881.1666   -0.113143];

DIY = day(datetime('31-Dec-1880'),'dayofyear')           % Leap Year!

DIY = 366

DOY = rem(A(:,1),1)*DIY;
HOD = rem(DOY,1)*24;
DT = datetime([fix(A(:,1)) zeros(size(A(:,1)))+1 fix(DOY)+1 fix(HOD) fix(rem(HOD,1)*60) fix(rem(HOD,1)*60)], 'Format','yyyy-MMM-dd HH:mm:ss')

DT = 15×1 datetime array
   1880-Jan-01 00:00:00
   1880-Jan-31 12:35:35
   1880-Mar-01 23:24:24
   1880-Apr-01 12:00:00
   1880-May-02 00:35:35
   1880-Jun-01 11:24:24
   1880-Jul-02 00:00:00
   1880-Aug-01 12:35:35
   1880-Aug-31 23:24:24
   1880-Oct-01 12:00:00
   1880-Nov-01 00:35:35
   1880-Dec-01 11:24:24
   1881-Jan-01 00:00:00
   1881-Jan-31 12:35:35
   1881-Mar-02 23:24:24

This appears to produce the correct result, although I did not rigorously check it.

NOTE to MathWorks — Would it be possible to implement this as an option?

.

[Stephen23]

"Would it be possible to implement this as an option?"

See my request and Staff response here: https://www.mathworks.com/matlabcentral/answers/1658145-decimail-years-date-to-juliandate#comment_2017000

[Star Strider]

I’d forgoten about that.

[Laura]

Thank you for your help Star Strider!

[Star Strider]

As always, my pleasure!

One note about the precision of the times is that with decimal precison of years:

fprintf('Time Precision = %.2f minutes\n', 366*24*60 * 1E-4)

Time Precision = 52.70 minutes

So the time is essentially in 52.7 minute or 0.878 hour intervals.

.