Setting time ticks in plot

Hello

I have made a Matlab plot based on a data vector. On the x-axis should be the time and on the y-axis the value. For each value I have a timestamp in milliseconds. I would like to have on the x-axis a tick every say 5min, say 16:05, 16:10, 16:15 and so on (16:05 means 4pm and 5mins). The time distance between the values is not equal.

How can this be done?

An example of a data vector is (first column timestamp, second column value):

    27634517312999, 1.1111809015274048
    27658503234656, 0.7998865246772766
    27662988099446  0.7806665897369385
    27664499628612  0.7781039476394653
    27950691973920  0.8562135696411133
    27970195902662  0.8036822080612183
    27973194252661  0.7908696532249451
    ....

[Jan]

If the first column are really milliseconds, the shown data have been recorded over almost 11 years. Plotting them with tick labels all 5 minutes will be very ugly.

(27973194252661 - 27634517312999) / 1000 ...  % seconds
/ 86400 ... % days
/ 365       % years

Do you mean nano-seconds?

Answer 1

[Jan]

data = [27634517312999, 1.1111809015274048; ...
  27658503234656,     0.7998865246772766; ...
  27662988099446,     0.7806665897369385; ...
  27664499628612,     0.7781039476394653; ...
  27950691973920,     0.8562135696411133; ...
  27970195902662,     0.8036822080612183; ...
  27973194252661,     0.7908696532249451];
Time  = data(:, 1) / (1000 * 86400);  % Milliseconds -> datenum format
Ticks = (ceil(data(1,1) / 300e3) : floor(data(end,1) / 300e3)) * 300 / (1000 * 86400);
% Far too many ticks to be drawn!

% axes('XTick', Ticks, 'NextPlot', 'add');
plot(Time, data(:, 2));
datetick('x', 'HH:MM', 'keepticks');

[Sepp]

When I do Time = data(:, 1) / (1000 * 86400); I'm getting 17397 for every timestamp value. By the way, the milliseconds measurement are absolute measurements for example 27658503234656 represents Mon Jun 18 2846 14:33:54 GMT+0100.

I think I have to be more clear. Each value has an assigned absolute timestamp in milliseconds which represents the time elapsed from 1970 (I think). I have gathered this values by `System.currentTimeMillis()` call from Java. For example 27658503234656 corresponds to Mon Jun 18 2846 14:33:54 GMT+0100. The values span rougly a range of one hour (the same year, day etc.). That means the first timestamp is 27658501657000 (representing Mon Jun 18 2846 14:07:37 GMT+0100) and the last timestamp is 27658504995000 (representing Mon Jun 18 2846 15:03:15 GMT+0100). I'm only interested in 14:07 until 15:03. On my x-axis the first label should be at 14:10 and then there should be labels every 5 min, i.e. 14:15, 14:20 etc. The last label is at 15:00.

How can this be done?

[Jan]

 When I do Time = data(:, 1) / (1000 * 86400); I'm getting 17397
 for every timestamp value

Do you? Please post the corresponding code.

Time  = data(:, 1) / (1000 * 86400);
Time(1)
        319843.950381933
diff(Time)
        277.614833993022
        51.9081572916475
        17.4945505324285
        3312.41140402778
        225.739915995393
        34.7031249884167

I do not see a 17397 (in which units?)

If 27658503234656 means 18-Jun-2048 14:33:54 the number are in fact the milliseconds since 01-Jan-1970. Then, as said already, your data set concerns a period of 10.7 years and ticks every 5 minutes will be an unreadable pile of pixels.

[Jan]

@Sepp: Did you try my code then?

Answer 2

[Peter Perkins]

The numbers in your example data don't match the numbers in your explanation:

>> x = [ ...
    27634517312999, 1.1111809015274048
    27658503234656, 0.7998865246772766
    27662988099446  0.7806665897369385
    27664499628612  0.7781039476394653
    27950691973920  0.8562135696411133
    27970195902662  0.8036822080612183
    27973194252661  0.7908696532249451];
>> data = array2table(x,'VariableNames',{'TimeStamp','X'});
>> data.TimeStamp = datetime(data.TimeStamp/1000,'ConvertFrom','posixtime')
data =
  7×2 table
         TimeStamp             X   
    ____________________    _______
    13-Sep-2845 22:48:32     1.1112
    18-Jun-2846 13:33:54    0.79989
    09-Aug-2846 11:21:39    0.78067
    26-Aug-2846 23:13:48     0.7781
    21-Sep-2855 09:06:13    0.85621
    04-May-2856 02:51:42    0.80368
    07-Jun-2856 19:44:12    0.79087

As others have said, this spans 11 years, and labelling ticks at 5min intervals makes no sense. If you do have data that count ms since 1970, and that span about an hour, do the above, and then start from

   plot(data.TimeStamp,data.X)

Depending on what release of MATLAB, setting the ticks to every 5min is different but generally easy.