changing minutes after midnight into a datetime array

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AA 2017-10-26

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评论： Walter Roberson 2017-11-20

Suppose you have the matrix minutesaftermid which contains integers that represent the minutes after midnight, e.g. 1,2,3,4,5,6,7,......

How do I convert this format to a datetime array.

t = datetime(Y,M,D,H,MI,S,MS), but I only needs the MI.

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Answer 1

per isakson 2017-10-26

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编辑：per isakson 2017-10-26

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"but I only need the MI" I don't think you can avoid the date and time.

X = 60*[1,2,3,4,5,6,7];
T = datetime( X, 'ConvertFrom','epochtime', 'Epoch','2000-01-01' )
T = 
Columns 1 through 4
   2000-01-01 00:01:00   2000-01-01 00:02:00   2000-01-01 00:03:00   2000-01-01 00:04:00
Columns 5 through 7
   2000-01-01 00:05:00   2000-01-01 00:06:00   2000-01-01 00:07:00

and

>> T.Minute
ans =
     1     2     3     4     5     6     7

Remark: the year 2000 is a leap year.

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Answer 2

Walter Roberson 2017-10-26

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datetime('today') + minutes(minutesaftermid)

if you wanted it to be relative to today (local time)

If you just need minutes after midnight and not any particular day, you should probably be leaving it as a duration array instead of a datetime array.

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Answer 3

Peter Perkins 2017-11-16

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datetimes are dates+times. As Walter says, unless you also have a set of dates, or you want 'today', then you likely want a duration array, and so just call the minutes function to create one.

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Peter Perkins 2017-11-20

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Ah, right. So you can either add minutes (as you showed), or if you have the date portion as numeric values, you can use the "roll-over" behavior built into the constructor:

>> datetime(2017,11,1:3,0,[1430 1440 1450],0)
ans = 
  1×3 datetime array
   01-Nov-2017 23:50:00   03-Nov-2017 00:00:00   04-Nov-2017 00:10:00

Walter Roberson 2017-11-20

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I might...

T = datetime(2017,11,1:3,0,[1430 1440 1450],0, 'TimeZone', 'local');
[H, M] = hms(T);
mins_since_midnight = H * 60 + M

... though I would want to double-check outputs when there are time zone changes. I have now gotten myself confused about what "minutes since midnight" even means when there are time-zone changes.

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