How do I find the number of hours?

Hello,

I have a matrix A with dimensions 35000X1 (datetime). There are hours in matrix A.

For example, 01:00, 05:00, 17:00, 23:00, 05:00, 09:00, ....

How can I find the number of each hour in matrix A. That is, how many hours are there that correspond to 00:00, 01:00,02:00,03:00, .... 21:00,22:00,23:00. Your help is important.

Answer 1

[Steven Lord]

I have a matrix A with dimensions 35000X1 (datetime). There are hours in matrix A.

For example, 01:00, 05:00, 17:00, 23:00, 05:00, 09:00, ....

Are these a datetime array or a duration array?

thisIsADatetime = datetime('now', 'Format', 'HH:mm')

thisIsADatetime = datetime
   12:05

thisIsADuration = duration(12, 5, 0, 'Format', 'hh:mm')

thisIsADuration = duration
   12:05

These are not the same, despite looking the same. The thisIsADatetime array has a date associated with it, while thisIsADuration does not. If it's a datetime array you probably want to calculate the time since midnight and compute histcounts on the resulting duration array.

dt = datetime('now') + days(randi([-2 2], 10, 1)) + hours(2*randn(10, 1))

dt = 10×1 datetime array
   23-Jul-2021 11:09:17
   20-Jul-2021 08:23:33
   22-Jul-2021 12:42:30
   21-Jul-2021 12:43:33
   19-Jul-2021 14:33:25
   21-Jul-2021 13:13:11
   20-Jul-2021 12:20:07
   19-Jul-2021 11:25:52
   23-Jul-2021 13:16:16
   20-Jul-2021 11:35:16

timeSinceMidnight = dt - dateshift(dt, 'start', 'day')

timeSinceMidnight = 10×1 duration array
   11:09:17
   08:23:33
   12:42:30
   12:43:33
   14:33:25
   13:13:11
   12:20:07
   11:25:52
   13:16:16
   11:35:16

These two histogram plots look very different, since one is binning by hours and one by days.

histogram(timeSinceMidnight, 6)

histogram(dt, 6)

Answer 2

[Mudit Chaturvedi]

Hi!

I understand you are trying to find the frequency of each element in a matrix.

You can use unique() function to get the unique elements and then calculate their frequency using histc or histcounts function

a = unique(A);
sol = [a,histc(A(:),a)];

Please refer to this Matlab Answers link for more information.

Answer 3

[stelios loizidis]

Another question I have is if I have table A but the available data are as follows: 1/2/2014 01:00, 4/5/2014 05:00, 6/8/2014 16:00,... How can I calculate the frequency that the hours appear regardless of the date.

[Steven Lord]

See timeSinceMidnight in my answer above.

[stelios loizidis]

In the histogram I want each bar to contain the values for each hour. That is, the first bar contains the values from 0000-0059, the second bar contains the number of hours from 0100-0159 and so on. So instead of 6 what number should I put?

[Steven Lord]

Use a vector of bin edges.

dt = datetime('now') + hours(24*rand(10, 1))

dt = 10×1 datetime array
   22-Jul-2021 00:35:06
   22-Jul-2021 04:14:00
   21-Jul-2021 23:30:36
   22-Jul-2021 03:32:47
   22-Jul-2021 09:54:42
   22-Jul-2021 02:09:19
   21-Jul-2021 18:09:34
   21-Jul-2021 18:48:10
   22-Jul-2021 07:20:03
   21-Jul-2021 18:17:55

timeSinceMidnight = dt - dateshift(dt, 'start', 'day')

timeSinceMidnight = 10×1 duration array
   00:35:06
   04:14:00
   23:30:36
   03:32:47
   09:54:42
   02:09:19
   18:09:34
   18:48:10
   07:20:03
   18:17:55

histogram(timeSinceMidnight, hours(0:24))
xticks(hours(0:24))

You might want to only display every other tick or change the Format property of the duration array that you pass into xticks.

[stelios loizidis]

Thanks for the valuable help !!!!