Load date/time data and being recognized for further time related subtraction/addtions

I have a text data file, which includes timestamp like 20150727084239.533 which represent 2015-07-27 08:42:39.533. And I have two questions when dealing with these. 1. how can I use textscan and have it recognized as time? I have the current code shown below, and it only load into the data array as numbers.

Load Vehicle A_0727_L2 Timestamp

filename='Vehicle A_0727_1200.txt';
fid=fopen(filename,'r');
for k=1:2;
  tline=fgetl(fid);                                
end
timestamp1200=zeros(1,7931);
t=1;
while tline~=-1
  datestr=regexp(tline,'(?<=STime="20150727).*(?=" ETime)','match');
  tempdata2=textscan(datestr{1},'%f');
  timestamp1200(:,t)=tempdata2{1};

    t=t+1;
    tline = fgetl(fid);
end
fclose all;

When I use %{HH:mm:ss.FFF}D to replace %f, system returns the following errors:

Error using textscan
Unable to read the DATETIME data with the format 'HH:mm:ss.FFF'. If the
data is not a time, use %q to get string data.
Error in C_July27_L2_Data (line 39)
  tempdata2=textscan(datestr{1},'%{HH:mm:ss.FFF}D');

2. How do I use the load time to perform subtraction like 463 seconds from the loaded data, etc.

thanks!

Answer 1

[Derick Yang]

Try using the datetime function instead of textscan. In your case, you can use the following format:

tempdata2 = datetime(datestr{1}, 'InputFormat', 'yyyyMMddHHmmss.SSS')

Note that this will give you a datetime object. With a datetime object you can perform date arithmetic. To subtract from your date object:

 tempdata2 - seconds(463).

[Ivy Chen]

When I using the date time function and replace with the line above, receive a following error:

Error using A_July27_L2_Data (line 42)
Cell contents reference from a non-cell array.

Any suggestion?

[Derick Yang]

This error means you need to reference datestr as a matrix rather than a cell array, using parentheses. Instead of datestr{1}, use datestr(1)

[Ivy Chen]

I replace the {} with parentheses, as following

Load Vehicle A_0727_L2 Timestamp

filename='Vehicle A_0727_1200.txt';
fid=fopen(filename,'r');
for k=1:2;
  tline=fgetl(fid);                              
timedata=zeros(1,7931);
t=1;
while tline~=-1
  datestr=regexp(tline,'(?<=STime=").*(?=" ETime)','match');
  tempdata2=datetime(datestr(1), 'InputFormat', 'yyyyMMddHHmmss.SSS');
  timedata(:,t)=tempdata2(1);
  t=t+1;
  tline = fgetl(fid);
end

But it now show a different error message as following:

The following error occurred converting from datetime to double:
Undefined function 'double' for input arguments of type 'datetime'. To convert from datetimes to numeric,
first subtract off a datetime origin, then convert to numeric using the SECONDS, MINUTES, HOURS, DAYS, or
YEARS functions.
Error in Timestamp_Data (line 13)
  timedata(:,t)=tempdata2(1);

Answer 2

[KL]

You could do it just by reading it as a string at first and then convert that string using datestr,

>> s = '20150727084239.533';
>> date = datestr([s(1:4),'-',s(5:6),'-',s(7:8),' ',s(9:10),':',s(11:12),':',s(13:end)])

date =

      '27-Jul-2015 08:42:39'