tic, 
for i=1:1000 
    dateNum=dtstr2dtnummx({'2010-12-12 12:21:12.123'},'yyyy-MM-dd HH:mm:ss.FFF');
end; 
dateNum
toc
 
dateNum =
          734484.514722222
 
Elapsed time is 0.099181 seconds.
 
% Slower - using datenum
tic
for i=1:1000 
    dateNum=datenum({'2010-12-12 12:21:12.123'},'yyyy-mm-dd HH:MM:SS.FFF');
end; 
dateNum
toc
 
dateNum =
          734484.514723646
 
Elapsed time is 0.172265 seconds.

The difference is the added millisecond value. Even adding the “.FFF” to the format string doesn’t seem to catch the milliseconds in the faster case. This must happen outside of the dtstr2dtnummx function.

Any idea where dtstr2dtnummx has disappeared to in the newer versions. Can’t find it in 2015a, for example. I know it’s there because I can call it but for the life of me I can’t find it.

Regards,
Phil

You want to compute the vector A and become the results in the variable Result:

Result=datestr(A); % To avoid

Use the unique function before:

[b, m, n] = unique(A); % Reduce your vector A
b=datestr(b); % Apply your function to b which is much smaller
Result=b(n,:); % Assign it to a vector the same size as A

For a vector A with a lot of same values it saved my life

The built-in DATENUMMX converts [1 x 6] date vectors 4 times faster than DATENUM. It is at least included in Matlab 5.3 to 2009a – I cannot check this in newer versions. As said already, the source code datenummx.c was shipped with Matlab 6.5.

In general the basic lesson here, as elsewhere in Matlab, is that wherever we can remove unnecessary input formats, options and validity checks, this could greatly increase the performance.

DATENUM: 0.93 sec, DTSTR2DTNUMMX: 0.21 sec, DateStr2Num: 0.0087 sec

And for a {1 x 1000} cell string:

DATENUM: 2.52 sec, DTSTR2DTNUMMX: 1.77 sec, DateStr2Num: 0.027 sec

The speed is based on two methods: 1. the format has to be specified by a very limited set of 6 most common formats. 2. The value is not checked for validity: While DATENUM and DTSTR2DTNUMMX recognize ‘2011-04-180’ more or less correctly as 179th day after 2011-04-01, DateStr2Num fails and does even not catch ‘2011-04-AB’ as an error. To calculate the fractional part for ’25:61:62′, the overflow can be ignored fortunately.

Therefore, if you know that the date string is valid, a very simple C-code can be 100 times faster than DATENUM and 25 times faster than DSTR2DNUMMX.

The C-Mex DATENUMMX.c was part of Matlab 6.5. What a pitty that modern Matlab versions include less of such cookies.

Kind regards, Jan