MatLAB noob here..
I have a 2 column matrix with start/end (in seconds) times - in a 2 column matrix.
I also have a single column matrix of time stamps. How do I find the time stamps that occur in each interval?
Not going to put any code here, as you provided none.
There are some alternatives, this is the most straight forward (though might not be the most efficient for the computer):
Use a for loop, for each line of your start/end matrix, and for each do another for loop for each element in your time stamp matrix, and assess, using if function, if each time stamp is between start and end times.
If you don't know how to use FOR and IF, type help FOR, help IF and find out. Or google it
Related
I've got time series data in TimescaleDB from smart meters, the Energy value is stored as a counter.
I have 2 questions:
1) How do I calculate the difference between each row of energy values so I can just see the increase minute by minute for each row?
2) I've got this in 1 minute intervals and I'd like to aggregate as 30m, 60m etc. What's the best way of achieving this?
Thanks in advance for any help you can give me.
There are a couple of challenges here. First, you have to make sure that the intervals of your counter indexes are constant (think communication outages,...) . If not, you'll have to deal with the resulting energy peaks.
Second, your index will probably look like a discrete jigsaw signal, restarting at zero once in a while.
Here's how we did it.
For 2), we use as many continuous aggregates on the indexes as we require resolutions (15min, 60min,...). Use locf where required.
For 1) we do the delta computation on the fly. Meaning that we query the db for the indexes and then loop through the array to compute the delta. This way we can easily handle the jigsaw and peaks.
I've just got an answer to my question, which is very similar to your Part 1, here
In short, the answer I got was to use a before_insert trigger and calculate the difference values on insertion, storing them in a new column. This avoids needing to re-calculate deltas on every query.
I extended the function suggested in the Answer by also calculating the delta_time with
NEW.delta_time = EXTRACT (EPOCH FROM NEW.time - previous_time);
This returns the number of seconds which have passed, allowing you to calculate meter power reliably.
For Part 2, consider a Continuous Aggregate with time buckets as suggested above
I am pretty new to Matlab and I could use some help. I have about 50k rows of data. What I would like to do is, that it would take the first number of the data, divide it by 12 and repeat the result 12 times then it would move on to the second number and do the same and so on and on till the end.
Best regards
I am relatively inexperienced with matlab, as I only use it occasionally. I am trying to plot a large range of values against time and I am running into some problems.
The data, which is from a text file, with about 55000 entries, gives the information in the following format:
year month day hour minute second value
The seconds column has accuracy of 6 decimal places and there are about 24hrs worth of data.
What I want to do is plot the values against time, which works fine. However as a result of my code below, the x-axis has label ticks in serial date number format, which is not very useful when looking at the figure. I want to change the labels to something more useful such intervals of hours. However I am not sure how to go about doing this.
Here is the code:
A = dlmread('data.txt',' ');
time = datenum(A(:,1),A(:,2),A(:,3),A(:,4),A(:,5),A(:,6));
scatter(time,A(:,7),1)
axis([min(time) max(time) min(A(:,7)) max(A(:,7))])
I found a solution here: matlab ticks with certain labels however, the process here is manual and with so much information I don't want to do this manually. How would I automate this process? or is there a better way to do what I am trying to achieve?
EDIT: I also found this method: http://www.mathworks.com/help/matlab/ref/datetick.html#btpnuk4-1, however, I dont want to show the actual date, I rather want to show intervals of time, ie an hour or 30 minutes.
EDIT 2: I have found a somewhat satisfactory solution. It could still be improved upon, so I don't know if I should submit this as an answer to my own question or not, but here it is:
A = dlmread('data.txt',' ');
time = datenum(A(:,1),A(:,2),A(:,3),A(:,4),A(:,5),A(:,6));
temp= time(1);
timediff = time - temp;
scatter(timediff,A(:,7),1)
axis([min(timediff) max(timediff) min(A(:,7)) max(A(:,7))])
datetick('x', 'HH')
This takes the original time vector in serialized time format and subtracts the first time from all the subsequent times to get the difference. The it uses the datetick function to to convert that to hours. It isn't ideal because instead of 24 hours it goes back to 00, but its the best I have tried thus far.
With reference to the other article, you will have to follow the same method but in order to automate the process you'll need to form the vectors of xtick and xticklabels as you read in the data and after you've plotted the data change the xticks and xticklabels.
Its not difficult what you're trying to do, but I will need more details of how you want to organize the ticks to be able to exactly say the steps that you'd have to follow
Matlab serial time is simply days since January 1, 0000, so your timediff variable is really elapsed days (and fractions thereof) since the start of your experiment. If you want your x ticks to be elapsed hours you could multiply timediff by 24.
scatter(timediff * 24, values)
This avoids the weirdness that can arise when using datetick as well.
Good morning,
I have a question about the time execution of a script on Matlab. Is it possible to know previously how long spend the execution of a script before running it (an estimated time, for example)? I know that with tic and toc command, among others, is it possible to know the time at the end but I don't know if it's possible to know it before.
Thanks in advance,
It is not too hard to make an estimate of how long your calculation will take.
You already know how to record calculation times with tic and toc, so now you can do this:
Start with a small scale test (example, n=1) and record the calculation time
Multiply n with a constant k (I usually choose 2 or 10 for easy calculations), record the calculation time
Keep multiplying with n untill you find a consistent relation: 'If I multiply my input size with k, my calculation time changes like so ...'
Now you can extrapolate your estimated calculation time by:
calculating how many times you need to multiply input size of the biggest small scale example to get your real data size
Applying the consistent relation that you found exactly that many times to the calculation time of your biggest small scale example
Of course this combines well with some common sense, like if you do certain things t times they will take about t times as long. This can easily be used when you have to perform a certain calculation a million times. Just interrupt the loop after a minute or so, if it is still in the first ten calculations you may want to give up!
I have a MySQL table with over 6 million records, each with a epoch timestamp. I need to plot all the timestamps across time of day. In other words, I need to see how many timestamps are between 7am and 8am, 8am to 9am, etc - for all 24 hour blocks in day. I do not need them plotted by day of the week or month, just time in the day. Each timestamp is in UTC.
can someone help me?
You could use MySQL's FROM_UNIXTIME function to get date strings from the database, and dump the results into a file, which you can subsequently read into MATLAB. Next, one of the ways to extract the time of day of each record is to use MATLAB's datevec function, to get each component of the date string seperately:
datevec('2007-11-30 10:30:19')
ans =
2007 11 30 10 30 19
For instance, if you read in the data as one long vector with date strings, you could apply datevec to this vector, and subsequently grab the 'hour column' of the resulting matrix. Then, you can make a histogram of the counts using the hist or histc functions, depending on whether you want to specify bin centers or bin edges. If you have an hour column H, something like hist(H, 0:23) should work. The histc function might be a bit more natural for the nature of your data, but is slightly more involved; check the documentation.