parsing a time stamp without a colon

Hi everyone, I'm having trouble with a text parsing operation

I have a large vector of timestamps which are listed in military time, but without colons, like this

1520 1525 1530 etc.

but also

0 05 10

and

130 135 etc.

I need to put in :'s appropriately so that I can get this read to serial date time. How to do this? I am guessing it's a regexp thing, but I can't figure out the right syntax. Or is there an option under datestr / datenum / datevec?

I tried datestr with the times as they are (and the correct doy2date, which turned out well) and this just gives me back that every single time is at 0:00:00 which will not do, since this is sensitive streaming sensor data.

Thanks! Fox P. OSU

[Walter Roberson]

To check: you want 1520 to be 15:20? And you want 130 135 to be 01:30 01:35 ? What about 0 05 10? Are those to be 00:00 and 00:05 and 00:10 ?

Answer 1

[Walter Roberson]

Prefix each time with 3 '0's. Then take the last 4 characters. You can datenum('HHMM') the result without needing to put in a colon.

But do be careful: when you do not specify a year, the time will be interpreted relative to Jan 1 of the current year.

I would therefor suggest you use a different approach: str2double() the string. The minutes are the result mod 100, and the hours are floor(result / 100). You can then construct datevec structures of them with any appropriate values in the year month day slots, and datenum() a bunch of them at once. Or, of course, just do a direct calculation (hours * 60 + minutes) / (365 * 24 * 60 * 60). [Except in leap years.]

Answer 2

[Siddharth Jose]

timestring=num2str(time);                 %This process will add blank spaces at zero posistion .eg:'930' will end up as '_930' 
timestring(timestring == ' ') = '0';              %To replace the blank spaces with zeros. 
%Here ends the answer to your question. optionally to create a proper datetime array follow the rest.
datestring=datestr(date);
dtcombined=datestring+""+timestring;  %To avoid strcat limitations. Works on Matlab 2017b and later
datentime= datetime(dtcombined,'InputFormat','dd-MM-yyyyHHmm'); 

[Walter Roberson]

The loop

for i = 1:length(timestring)                %To replace the spaces with zeros. 
  if timestring(i)==' '
   timestring(i) = '0';
  end
end

can be replaced with no loop with

timestring(timestring == ' ') = '0';

Note that the code will fail if it happens that all of the entries are less than 1000 . Leading spaces will only be put in place by num2str() to make all of the entries the same length, not any particular length.

[Siddharth Jose]

Well, the only reason to have added the following code segment

for i = 1:length(timestring)                %To replace the spaces with zeros. 
  if timestring(i)==' '
   timestring(i) = '0';
  end
end

is to add zero's in the blank spaces that occur before 1000 as matlab converts '930' to '_930'. '_'-symbolic for space. And you'll have to modify it a bit for times between midnight and 00:59.

In all other cases it works.

Thank you for mentioning

"timestring(timestring == ' ') = '0'; "

does the job better.I've edited my answer too.:)

[Walter Roberson]

You would need to modify for times between 00:00 and 09:59 -- unless, that is, there happened to be at least one entry from 10:00 onwards in the mix.

[Siddharth Jose]

:D True.

[Walter Roberson]

 timestring = num2str(time, '%04d');

would not have the range problems and would not require any replacement of ' ' with '0'