How to average multiple vectors of different lengths?
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I am taking multiple measurements (50~100) and want to take the mean of the measurements.
Here is how I am going about doing it: I define zero matrix of certain dimension to begin with, for example, zeros(1000,3,50) - each measurement is a matrix of 1000 rows and 3 columns. In this case, the 3rd dimension of 50 is to keep track of the 50 iterations of the measurement.
The issue is that, some measurement will end at row index 500 whereas some others at other row indices. If the longest measurement record the last value at row index 804, then I need to replicate all other measurements' last values up until row index 804 before taking appropriate average of all measurements.
Any ideas would be greatly appreciated!
Thanks,
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Answers (2)
Iain
on 17 Jun 2013
When you DON'T have a measurement, ensure that it is "NaN", when you come to take the average, use "nanmean", which ignores the NaN's in the calculations.
nanmean (or mean) can operate on a single dimension at a time...
2 Comments
Iain
on 18 Jun 2013
Edited: Iain
on 18 Jun 2013
Ok.
Don't use nans, use zeros, take the first "slice", and take the "diff" of the rest of it
f = dataset(:,:,1);
d = diff(dataset,1,3);
get rid of the negatives (assuming your data is purely monotonic
d(d<0) = 0;
Put them together
f(:,:,2:(size(d,3)+1)) = d;
Take the cumulative sum:
f = cumsum(f,3);
means = mean(f,chosen_dim);
John
on 18 Jun 2013
Are any of your measurements exactly 0? Or, are any of them -1? Instead of initializing with zeros, you could initialize with M = -1*ones(1000,3,50). Then, you can do something like
for i = 1:50
[afterlastrow,c] = find(m(:,:,i)==-1);
lastrow = afterlastrow(1)-1;
m(m(:,1,i)==-1,1,i) = m(lastrow,1,i);
m(m(:,2,i)==-1,2,i) = m(lastrow,2,i);
m(m(:,3,i)==-1,3,i) = m(lastrow,3,i);
end
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