How do I keep MATLAB from truncating my date numbers?
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I have data (a lot of data: hundreds of thousand of observations) recorded at one minute intervals over several months in an Excel spreadsheet. The code I use to get the time is:
[NUM,TXT,RAW] = xlsread(filename)
time_string = TXT(:,1);
time = datenum(time_str);
The problem: the time strings in TXT are read correctly (Example: '1/1/2014 12:02:00 AM'), but in the step where they are converted to numbers, MATLAB doesn't keep anything to the right of the decimal.
For example, '1/1/2014 12:02:00 AM' should be "735600.0013888" (found from converting a single date from the time string above - it works for that), but when converting the whole list "time_string", MATLAB truncates this and all the other dates to 735600, which converts to 01-Jan-2014.
Why does it do that? How can I make MATLAB keep the whole number?
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the cyclist
2014년 6월 3일
Are you able to give a small, self-contained example that we can run, that exhibits the problem?
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the cyclist
2014년 6월 5일
The documentation for datenum states that if you are converting multiple date strings, then they all have to be in the same format. So, if you change your input to
'1/1/2014 12:00:00 AM'
'1/1/2014 12:01:00 AM'
'1/1/2014 12:02:00 AM'
'1/1/2014 12:03:00 AM'
'1/1/2014 12:04:00 AM'
'1/1/2014 12:05:00 AM'
'1/1/2014 12:06:00 AM'
'1/1/2014 12:07:00 AM'
'1/1/2014 12:08:00 AM'
'1/1/2014 12:09:00 AM'
then you will get the answer you expect.
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the cyclist
2014년 6월 6일
FYI, I do also recommend using the second argument, specifying the date format, especially if the vectors are long. On my machine, the code
d = '1/1/2014 12:00:00 AM';
dd = repmat(d,10000,1);
tic datenum(dd);
toc
takes over 4 seconds, while
d = '1/1/2014 12:00:00 AM';
dd = repmat(d,10000,1);
tic
datenum(dd,'mm/dd/yyyy HH:MM:SS AM');
toc
only takes less than 0.2s.
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the cyclist
2014년 6월 3일
I think this is a longshot, but does it help if you add the second argument, specifying the date string format?
datenum('1/1/2014 12:02:00 AM','mm/dd/yyyy HH:MM:SS')
This should also have the benefit of speeding up that line a lot. (At least, that is my experience.)
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