DateStr2Num

Convert date string to date number - CMex: much faster than DATENUM

Description

DATESTR2NUM - Fast conversion of DATESTR to DATENUM

The builtin DATENUM command is very powerful, but if the input is known to be valid and formatted exactly, a specific MEX can be much faster:
For single strings DateStr2Num takes <1% of the processing time of DATENUM (even with specified date format), for a {1 x 10000} cell string, DateStr2Num needs 0.17% to 2.7% of the DATENUM time. (Matlab 2009a, MSVC 2008 using SSE2 optimization).

D = DateStr2Num(S, F)
INPUT:
  S: String or cell string in DATESTR(F) format.
      In opposite to DATENUM the validity of the input string is *not* checked,
      e.g. if month is in [1:12] and hour in [0:23].
  F: Integer number defining the input format. Accepted:
        0: 'dd-mmm-yyyy HH:MM:SS' 01-Mar-2000 15:45:17
        1: 'dd-mmm-yyyy' 01-Mar-2000
       29: 'yyyy-mm-dd' 2000-03-01
       30: 'yyyymmddTHHMMSS' 20000301T154517
       31: 'yyyy-mm-dd HH:MM:SS' 2000-03-01 15:45:17
      300: 'yyyymmddTHHMMSS.FFF'

OUTPUT:
  D: Serial date number.

EXAMPLE:
  C = {'2010-06-29 21:59:13', '2010-06-29 21:59:13'};
  D = DateStr2Num(C, 31)
  >> [734318.916122685, 734318.916122685]
  Equivalent Matlab command (but a column vector is replied ever):
  D = datenum(C, 'yyyy-mm-dd HH:MM:SS')

Precompiled Mex files: http://www.n-simon.de/mex

Tested: Matlab 6.5, 7.7, 7.8, 32bit, WinXP
Compiler: LCC 2.4/3.8, BCC 5.5, Open Watcom 1.8, MSVC 2008
        Compatibility to MacOS, Linux, 64 bit is assumed, but not tested.

See also: DateConvert (Jan Simon)
  http://www.mathworks.com/matlabcentral/fileexchange/25594

• MATLAB release: MATLAB 7.8 (R2009a)

[Reyna]

This is great. Is it possible to add millisec? Particularly to extend format 30 to yyyymmddTHHMMSS.FFF?

[Jan Simon]

@Reyna: The new '300' format contains milliseconds also.

[Nate Jensen]

Good function, I use it all the time. I am retarded at C though. Could you tell me how to run the C function from Matlab? Thanks.

[Nate Jensen]

Sorry, I'm retarded, I figured it out.

[Todd]

My bad. Like Nate, I figured it out - what a difference! The command:
mex -O DateStr2Num.c
Generated a DateStr2Num.mexw64 file and wham! My code was at 90s using datenum. Now that section takes 0.02s. Thanks!

[Saad]

Hi, thanks for writing this, it works great. But it seems like the C compiled version doesn't accept a char string? I have a char string of 1x25 which works with the normal .m function but I get a warning that the format is not acceptable within the compiled version. I have to use the cellstr() function to convert, before passing to the compiled version. In the end, the run time between compiled and .m function are the same. Anyway you can adapt this?

[Saad]

ignore my previous comment...the string had some trailing whitespace which was leading the c program to throw an exception.

[Jan Simon]

To convert a serial date number to a '2011-08-24 23:38:44' date string:
sprintf('%.4d-%.2d-%.2d %.2d:%.2d:%.2d', datevecmx(now, 1));

[Jonathan Sullivan]

Very nice submission. It is enormously faster than datenum. Another great file from Jan.