I have an array of Epoch times that include fractional (nanoseconds). I have reviewed Converting Epoch to Date in Matlab but still cannot seem to convert to the correct date. I must be missing something simple.
Example data:
1548348497.191261
I am using the code in the link above.
time_unix_nanos = 1548348497.191261;
millis = round(time_unix_nanos);
nanos = time_unix_nanos - 1e6 * millis;
time_matlab = round(864e5 * (millis - datenum('1970', 'yyyy')));
s = [datestr(time_matlab, 'yyyy-mm-dd hh:mm:ss.FFF;), num2str(nanos)];
fprintf('s: = %f\n',s);
Two desired outputs
Full date format: yyyy-mm-dd HH:mm:ss.SSS
Just time format: HH:mm:ss.SSS
Thanks in advance!
It seems you've mistaken the conversion of unixtime to matlab time with matlab time to unixtime.
time_unix_nanos = 1548348497.191261;
millis = round(time_unix_nanos / 1e6); % You had also a /1e6 missing here
nanos = time_unix_nanos - 1e6 * millis;
% The following line converts unix time to matlab time. The line you used was doing the opposite
time_matlab = datenum('1970', 'yyyy') + millis / 864e5;
% First desired date format
s1 = [datestr(time_matlab, 'yyyymmdd HH:MM:SS.FFF;'), num2str(nanos)]
% Second desired date format
s2 = [datestr(time_matlab, 'HH:MM:SS.FFF;'), num2str(nanos)]
gives
>> s1
'19700101 00:00:01.548;348497.1913'
>> s2
'00:00:01.548;348497.1913'
Related
I'm trying to convert an array of milliseconds and its respective data. However I want to do so in hours and minutes.
Millis = [60000 120000 180000 240000....]
Power = [ 12 14 12 13 14 ...]
I've set it up so the data records every minute, hence the 60000 millis (= 1 minimte). I am trying to plot time on the x axis and power on the y. I would like to have the x axis displayed in hours and minutes with each respective power data corresponding to its respective time.
I've tried this
for i=2:length(Millis)
Conv2Min(i) = Millis(i) / 60000;
Time(i) = startTime + Conv2Min(i);
if (Time(i-1) > Time(i) + 60)
Time(i) + 100;
end
end
s = num2str(Time);
This in attempt to turn the milliseconds into hours starting at 08:00 and once 60 minutes have past going to 09:00, the problem is plotting this. I get a gap between 08:59 and 09:00. I also cannot maintain the 0=initial 0.
In this scenario it is preferable to work with datenum values and then use datetick to set the format of the tick labels of your plot to 'HH:MM'.
Let's suppose that you started taking measurements at t_1 = [HH_1, MM_1] and stopped taking measurements at t_2 = [HH_2, MM_2].
A cool trick to generate the array of datenum values is to use the following expression:
time_datenums = HH_1/24 + MM_1/1440 : 1/1440 : HH_2/24 + MM_2/1440;
Explanation:
We are creating a regularly-spaced vector time_datenums = A:B:C using the colon (:) operator, where A is the starting datenum value, B is the increment between datenum values and C is the ending datenum value.
Since your measurements have been taken every minute (60000 milliseconds), then the increment between datenum values should be of 1 minute too. As a day has 24 hours, that makes 1440 minutes a day, so use B = 1/1440 as the increment between vector elements, to get 1 minute increments.
For A and C we simply need to divide the hour digits by 24 and the minute digits by 1440 and sum them up like this:
A = HH_1/24 + MM_1/1440
C = HH_2/24 + MM_2/1440
So for example, if t_1 = [08, 00], then A = 08/24 + 00/1440. As simple as that.
Notice that this procedure doesn't use the datenum function at all, and still, it manages to generate a valid array of datenum values only taking into consideration the time of the datenum, without needing to bother about the date of the datenum. You can learn more about this here and here.
Going back to your original problem, let's have a look at the code:
time_millisec = 0:60000:9e6; % Time array in milliseconds.
power = 10*rand(size(time_millisec)); % Random power data.
% Elapsed time in milliseconds.
elapsed_millisec = time_millisec(end) - time_millisec(1);
% Integer part of elapsed hours.
elapsed_hours_int = fix(elapsed_millisec/(1000*60*60));
% Fractional part of elapsed hours.
elapsed_hours_frac = (elapsed_millisec/(1000*60*60)) - elapsed_hours_int;
t_1 = [08, 00]; % Start time 08:00
t_2 = [t_1(1) + elapsed_hours_int, t_1(2) + elapsed_hours_frac*60]; % Compute End time.
HH_1 = t_1(1); % Hour digits of t_1
MM_1 = t_1(2); % Minute digits of t_1
HH_2 = t_2(1); % Hour digits of t_2
MM_2 = t_2(2); % Minute digits of t_2
time_datenums = HH_1/24+MM_1/1440:1/1440:HH_2/24+MM_2/1440; % Array of datenums.
plot(time_datenums, power); % Plot data.
datetick('x', 'HH:MM'); % Set 'HH:MM' datetick format for the x axis.
This is the output:
I would use datenums:
Millis = [60000 120000 180000 240000 360000];
Power = [ 12 14 12 13 14 ];
d = [2017 05 01 08 00 00]; %starting point (y,m,d,h,m,s)
d = repmat(d,[length(Millis),1]);
d(:,6)=Millis/1000; %add them as seconds
D=datenum(d); %convert to datenums
plot(D,Power) %plot
datetick('x','HH:MM') %set the x-axis to datenums with HH:MM as format
an even shorter approach would be: (thanks to codeaviator for the idea)
Millis = [60000 120000 180000 240000 360000];
Power = [ 12 14 12 13 14 ];
D = 8/24+Millis/86400000; %24h / day, 86400000ms / day
plot(D,Power) %plot
datetick('x','HH:MM') %set the x-axis to datenums with HH:MM as format
I guess, there is an easier way using datetick and datenum, but I couldn't figure it out. This should solve your problem for now:
Millis=6e4:6e4:6e6;
power=randi([5 15],1,numel(Millis));
hours=floor(Millis/(6e4*60))+8; minutes=mod(Millis,(6e4*60))/6e4; % Calculate the hours and minutes of your Millisecond vector.
plot(Millis,power)
xlabels=arrayfun(#(x,y) sprintf('%d:%d',x,y),hours,minutes,'UniformOutput',0); % Create time-strings of the format HH:MM for your XTickLabels
tickDist=10; % define how often you want your XTicks (e.g. 1 if you want the ticks every minute)
set(gca,'XTick',Millis(tickDist:tickDist:end),'XTickLabel',xlabels(tickDist:tickDist:end))
I am having some issues in Matlab to do with rounding errors with datetime typed variables.
I have an array, lets call it 't', and it is of type datetime.
Say for example, t(2) = 00:01:35.6889999, and t(1) = 00:01:35.3549042.
If I try to do t(2)-t(1), all I get is an answer of type 'duration' of 00:00:00 .
I would like to find the difference between these times and keep the precision!
Any help, or directions to links that directly cater/relate to an issue like this would be appreciated! I'm not that familiar with using datetime & duration typed variables in Matlab!
Extra info: I am using Matlab R2017a
Edit: I have Format Long; written in my script.
Precision is not being lost, you just need to change the display format.
The default display format is HH:MM:SS:
>> A = duration(0, 0, 0, 1.25) % 1.25 MS
A =
duration
00:00:00
You can modify the format to display fractional parts. For example:
>> A.Format = 's' % Seconds only
A =
duration
0.00125 sec
>> A.Format = 'hh:mm:ss.SSSSSSSS' % HMS, up to 9 fractional second digits
A =
duration
00:00:00.00125000
You can also use helper functions like milliseconds or seconds to return double arrays:
>> seconds(A)
ans =
0.0013
>> milliseconds(A)
ans =
1.2500
This should work if only seconds vary in the two dates
second(t(1))-second(t(2))
The duration object actually has the proper precision. It just doesn't display it unless you set the format.
>> dur = duration(t(2) - t(1), 'Format', 's')
dur =
duration
0.3341 sec
Whether you set the format or not, you can grab the seconds directly from the duration object.
>> format long
>> seconds(dur)
ans =
0.334095700000000
>> seconds(t(2) - t(1))
ans =
0.334095700000000
all
I wonder if there is a way to generate timestamp series in Matlab ?
I assume there will be a start time, a end time, and a frequency.
It is simple to generate normal series using 1:1:100 (1 to 100 by 1)
How I can use a similar way to generate a time stamp series?
For instance, I specify start time as 9am, up to 10am, I want to generate something like 9:00:00:000, 9:00:00:500, 9:00:01:000, ....
gaped by 500 millisecond
Or even better, include date as well.
Use datenum, the only problem you might have is that your colliding with a gap second/day or summer savings time if you're spanning a long time period (but I don't think that's implemented in datestr as you can read here).
Play around with datenum, now and datestr
starttime = datenum(2000, 1, 1, 9, 0, 0);
dt = 0.500/86400; % datenum is a serial time format with 1 = 1 day = 86400 sec
N = 5;
timevec = starttime + dt*(0:(N-1));
>> datestr(timevec, 'HH:MM:SS.FFF')
ans =
09:00:00.000
09:00:00.500
09:00:01.000
09:00:01.500
09:00:02.000
Starting from 2015a, you can use the milliseconds function to build a vector of timesteps between to time points:
start = datetime('2017/1/3 9:00:00:000','InputFormat','yyyy/MM/dd H:mm:ss:SSS');
step = milliseconds(500);
fin = datetime('2017/1/3 10:00:00:000','InputFormat','yyyy/MM/dd H:mm:ss:SSS');
time_vec = start:step:fin;
If you don't define the date explicitly it will choose the current date.
You can also have one structure for both the time and the data, you can use the timeseries class (using start from above):
data = rand(7201,1);
ts = timeseries(data,'Name','MyTs');
ts.TimeInfo.StartDate = start;
ts.TimeInfo.Units = 'milliseconds';
ts = setuniformtime(ts,'Interval',500);
This will create a time series object:
>> ts
timeseries
Common Properties:
Name: 'MyTs'
Time: [7201x1 double]
TimeInfo: [1x1 tsdata.timemetadata]
Data: [7201x1 double]
DataInfo: [1x1 tsdata.datametadata]
with the following time info:
>> ts.TimeInfo
tsdata.timemetadata
Package: tsdata
Uniform Time:
Length 7201
Increment 500 milliseconds
Time Range:
Start 03-Jan-2017 09:00:00
End 03-Jan-2017 10:00:00
Common Properties:
Units: 'milliseconds'
Format: ''
StartDate: '03-Jan-2017 09:00:00'
It depends on your needs, but you can consider using the combination of datetime() and one or many of days(), hours(), minutes(), seconds() etc. functions.
Lets write some code:
start=datetime(1985,07,13,9,0,0); % your start date
steps=seconds(0:0.5:100); % your vector with steps
timeseries=start+steps; % your time series
you can also set format for displaying data that meets your needs, to do so check datetime properties manual.
I have this code as part of my program to calculate the solar time. But my calculation using decimal time. And now, I need to display the result in clock time.
%To calculate solar time
stime = time + (((4*(Lloc-Lsm))+ Et)/60);
disp(['The true solar time is ' num2str(stime),'hr']); %To display the solar time
The answer goes like this:
The true solar time is 13.0501hr
How can I convert the time to clock time (12hr or 24 hr format). i.e the minute should multiply by 60 (0.0501*60min = 3.006) and the time should display as 13:03 or 1:03PM.
Appreciate your help. Thank you.
Regards, -researcher-
you can use the following
my_hour = floor(stime);
my_minute = round(mod(stime, 1) * 60);
disp(['The true solar time is ', num2str(my_hour), ':', num2str(my_minute)]);
Use datenum to convert to a serial date number and then datestr to build the string with appropriate format:
h = 13.0501; %// your computed decimal time
string = datestr(datenum([0 0 0 h 0 0]),14); %// or change "14" for other formats
The two formats you specify correspond to formats 13 through 16 in datestr (see link to the documentation above). For example, with format 14 the string is
>> disp(string)
1:03:00 PM
I would like to convert an elapsed number of seconds into HH:MM:SS format. Is there a built-in function for this, or do I have to write my own?
datestr is probably the function you are looking for. Express your time interval as a decimal fraction of a day, for example:
>> datestr(0.25, 'HH:MM:SS.FFF')
ans =
06:00:00.000
That is, one quarter of a day is 6 hours. If you want to transform intervals longer than a day this way you'll have to adjust the second argument, which formats the function's output, for example:
>> datestr(2.256789741, 'DD:HH:MM:SS.FFF')
ans =
02:06:09:46.634
The first argument to datestr could also be either a date vector or a date string rather than a date serial number. This should get you started, if you have problems ask another question or edit this one.
--
To convert a time in seconds using datestr, divide the value by 24*60*60.
Sample:
t1 = toc;
timeString = datestr(t1/(24*60*60), 'DD:HH:MM:SS.FFF');
I don't know a built-in function. However, there is a SEC2HMS on Matlab's File Exchange. Basically, it boils down to something like
function [hours, mins, secs] = sec2hms(t)
hours = floor(t / 3600);
t = t - hours * 3600;
mins = floor(t / 60);
secs = t - mins * 60;
end
If you also want to have it formatted, use a printf:
function hms = sec2hms(t)
hours = floor(t / 3600);
t = t - hours * 3600;
mins = floor(t / 60);
secs = t - mins * 60;
hms = sprintf('%02d:%02d:%05.2f\n', hours, mins, secs);
end
sec2hms(69.9904)
ans =
00:01:09.99
If you want to get the hours, minutes and seconds as doubles consider the following line of code:
seconds = 5000;
hms = fix(mod(seconds, [0, 3600, 60]) ./ [3600, 60, 1])
hms =
1 23 20
This line of code is more than 100 times faster than using the built-in datestr funciton.
nIterations = 10000;
tic
for i = 1:nIterations
hms = fix(mod(seconds, [0, 3600, 60])./[3600, 60, 1]);
end
sprintf('%f ms\r', toc / nIterations * 1000)
gives 0.001934 ms.
tic
for i = 1:nIterations
datestr(seconds/24/3600, 'HH:MM:SS');
end
sprintf('%f ms\r', toc / nIterations * 1000)
gives 0.209402 ms.
If you want from original second input, just convert it to a fraction of the day:
datestr(25/24/3600, 'DD-HH:MM:SS')
ans =
00-00:00:25
Just gives it for 25 seconds (as from tic/toc)