Matlab does plot datetime data (only hours) on wrong day

Question

Renan Deuter 2022-7-17

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1762320-matlab-does-plot-datetime-data-only-hours-on-wrong-day

评论： Steven Lord 2022-7-17

采纳的回答： Star Strider

Hello,

I have data from two sensors that I want to plot in the same window to compare differences in my X value.

I have them both stored in tables and use the datetime "HH:mm:ss.SS" format.

For example:

sensor1.Time = ['12:41:50.00'; '12:41:51.00'; ...]

sensor1.x = [0.01; 0.02; 0.02; ...]

and

sensor2.Time = ['12:42:05.46'; '12:42:05.49'; ...]

sensor2.x = [0.01; 0.02; 0.01; ...]

When I plot the data using

plot(sensor1.Time, sensor1.x) it plots the data in a window and adds todays date.

However, when I plot the other table it adds a random date (here: 15.07.2022).

If I plot both using hold on; the data then looks like this which is not very helpful:

How can I fix this date error and have the data aligned on one day?

Best Regards,

Renan

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Answer 1

Star Strider 2022-7-17

1
链接

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https://ww2.mathworks.cn/matlabcentral/answers/1762320-matlab-does-plot-datetime-data-only-hours-on-wrong-day#answer_1009435

在 MATLAB Online 中打开

Without having the data to experiment with, my only suggestion is to plot them after converting them to duration arrays (that itself is not as straightforward as I would like it to be, especially since duration arrays are limited to one day in length) —

Time1 = datetime(2022,7,15) + minutes(0:1439).'

Time1 = 1440×1 datetime array

15-Jul-2022 00:00:00 15-Jul-2022 00:01:00 15-Jul-2022 00:02:00 15-Jul-2022 00:03:00 15-Jul-2022 00:04:00 15-Jul-2022 00:05:00 15-Jul-2022 00:06:00 15-Jul-2022 00:07:00 15-Jul-2022 00:08:00 15-Jul-2022 00:09:00 15-Jul-2022 00:10:00 15-Jul-2022 00:11:00 15-Jul-2022 00:12:00 15-Jul-2022 00:13:00 15-Jul-2022 00:14:00 15-Jul-2022 00:15:00 15-Jul-2022 00:16:00 15-Jul-2022 00:17:00 15-Jul-2022 00:18:00 15-Jul-2022 00:19:00 15-Jul-2022 00:20:00 15-Jul-2022 00:21:00 15-Jul-2022 00:22:00 15-Jul-2022 00:23:00 15-Jul-2022 00:24:00 15-Jul-2022 00:25:00 15-Jul-2022 00:26:00 15-Jul-2022 00:27:00 15-Jul-2022 00:28:00 15-Jul-2022 00:29:00

Data1 = sin(2*pi*(0:numel(Time1)-1)/720);

Time2 = datetime(2022,07,18) + minutes(0:1439).'

Time2 = 1440×1 datetime array

18-Jul-2022 00:00:00 18-Jul-2022 00:01:00 18-Jul-2022 00:02:00 18-Jul-2022 00:03:00 18-Jul-2022 00:04:00 18-Jul-2022 00:05:00 18-Jul-2022 00:06:00 18-Jul-2022 00:07:00 18-Jul-2022 00:08:00 18-Jul-2022 00:09:00 18-Jul-2022 00:10:00 18-Jul-2022 00:11:00 18-Jul-2022 00:12:00 18-Jul-2022 00:13:00 18-Jul-2022 00:14:00 18-Jul-2022 00:15:00 18-Jul-2022 00:16:00 18-Jul-2022 00:17:00 18-Jul-2022 00:18:00 18-Jul-2022 00:19:00 18-Jul-2022 00:20:00 18-Jul-2022 00:21:00 18-Jul-2022 00:22:00 18-Jul-2022 00:23:00 18-Jul-2022 00:24:00 18-Jul-2022 00:25:00 18-Jul-2022 00:26:00 18-Jul-2022 00:27:00 18-Jul-2022 00:28:00 18-Jul-2022 00:29:00

Data2 = cos(2*pi*(0:numel(Time1)-1)/720);

figure

plot(Time1, Data1)

figure

plot(Time2, Data2)

figure

plot(Time1,Data1)

hold on

plot(Time2, Data2)

hold off

Time1.Format = 'HH:mm:ss';

Dur1 = duration(string(Time1)); % Convert To 'duration' Array

Time2.Format = 'HH:mm:ss';

Dur2 = duration(string(Time2)); % Convert To 'duration' Array

figure

plot(Dur1, Data1)

hold on

plot(Dur2, Data2)

hold off

Your data will likely work for a duration array, however if they go for longer than one calendar day, it might be necessary to convert the time values only to datenum vectors and plot the data against that instead.

.

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Star Strider 2022-7-17

@Renan Deuter — As always, my pleasure!

Steven Lord 2022-7-17

在 MATLAB Online 中打开

@Star Strider The behavior you described is correct, but it's not due to any issue with duration. It's due to the fact that the datetime data covers multiple days.

midnight = datetime('today')
midnight = datetime
   17-Jul-2022
dt = midnight + minutes([-5, 5])
dt = 1×2 datetime array
   16-Jul-2022 23:55:00   17-Jul-2022 00:05:00
dt.Format = 'HH:mm:ss'
dt = 1×2 datetime array
   23:55:00   00:05:00

If you extracted the duration data from the datetime array with timeofday, you could check for any large jumps. This would indicate crossing midnight and could be resolved by adding 24 hours.

tod = timeofday(dt)
tod = 1×2 duration array
   23:55:00   00:05:00
d = [0, diff(tod)]
d = 1×2 duration array
    00:00:00   -23:50:00
tod(d < 0) = tod(d < 0) + hours(24)
tod = 1×2 duration array
   23:55:00   24:05:00
check = midnight - days(1) + tod
check = 1×2 datetime array
   16-Jul-2022 23:55:00   17-Jul-2022 00:05:00

The check array looks like it matches the dt array.

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Answer 2

the cyclist 2022-7-17

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1762320-matlab-does-plot-datetime-data-only-hours-on-wrong-day#answer_1009420

The most fundamental fix to your issue is to explicitly use the modern datetime format for your times. Then, downstream functions that use them as inputs can be manipulated to control the display output.

Also, rather than "MATLAB randomly does something for some reason", one can generally find the exact behavior in the documentation for each function.