How can I compute the mean value over a time interval?

Hi veryone!

I have a matrix of 2 colums (one vector time, one vector values) and i'd like to compute the mean value over a time interval.

How can i do that?

thank you very much in advance

Answer 1

[Chad Greene]

Hi Anna, welcome to the forum.

With these types of questions it always helps if you can provide a minimal working example. But you explained the problem well enough that I think I can come up with one.

So you have a matrix M whose columns correspond to time and some dependent variable. Let's say M looks like this:

M = [(1:100)' (1:100)'.^2+randn(100,1)]; 

Plot the first and second colums to see what kind of data we're looking at:

plot(M(:,1),M(:,2))
xlabel time

To get the average over some interval, say between t = 55 and t=65, get the indices of that range:

ind = M(:,1)>=55 & M(:,1)<65; 

Then calculate the mean of column 2 over the interval:

mean(M(ind,2))

ans = 3.5481e+03

[anna bicchi]

Thank you very very much! :)

Answer 2

[Eric Sofen]

If you have, for example, data once per second for an hour and you want to calculate mean values for each minute, I'd recommend using a timetable to store the data and using the retime function. Something like this

% Synthetic data
t = timetable(seconds(0:3600)',rand(3601,1));

tAvg = retime(t,"minutely","mean");
tAvg.Time.Format = 'm' % Display times in minutes

[Coral Stancliffe-Caldicott]

Hi,

If I were to have data once every 30 minutes for a year and wanted to calculate mean monthly values how would I adapt the above code?

Thanks

[Eric Sofen]

retime(t,"monthly","mean")

The NewTimeStep positional argument lists the possible automatic aggregations around calendar unit. If you wanted to do something custom, you can also specify a new time vector. For example, if you wanted to average into 10-day bins, you might construct a time vector something like:

tvNew = t.Time(1):days(10):t.Time(end)
retime(t,tvNew,"mean")