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confusion during finding out the mean of a 3d vector

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SWARNENDU PAL
SWARNENDU PAL on 21 Jul 2021
Commented: SWARNENDU PAL on 21 Jul 2021
I have a 3d vector of size 1498x1498x24. I want to calculate the wholes mean of the vector. I have used two method and got two different result. If anyone please explain this part that will be really helpful. I am giving the code and corresponding result.
mean(mmr_timeseries,'all','omitnan')
Using this i got the value 970.8025. Then i used :
mean(mean(mean(mmr_timeseries,'omitnan'),'omitnan'),'omitnan')
In this case I got 884.2371. I think these two lines are equivalent but I got different result. If ant=yone could please explain this part that will be really helpful. Thank you.
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Accepted Answer

Chunru
Chunru on 21 Jul 2021
Edited: Chunru on 21 Jul 2021
A 2-d example (applicable to 3d in principle).
a=[1 2; 3 3; nan 4; nan nan]
a = 4×2
1 2 3 3 NaN 4 NaN NaN
% mean of [1 2 3 3 4] after omitting nans
mean(a,'all','omitnan')
ans = 2.6000
% mean for each column (omit nans)
mean(a,'omitnan')
ans = 1×2
2 3
% mean of the above vector , i.e. [2, 3]
mean(mean(a,'omitnan'),'omitnan')
ans = 2.5000
% The following is for 3d (not shown in this example)
mean(mean(mean(a,'omitnan'),'omitnan'),'omitnan')
ans = 2.5000
  5 Comments
SWARNENDU PAL
SWARNENDU PAL on 21 Jul 2021
I think 2nd one is the correct and more meaningful as it gives the mean of all numbers.

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More Answers (1)

Jonas
Jonas on 21 Jul 2021
the short answer:
your second approach takes mean values of means and the first approach takes the mean value of all elements
  2 Comments
SWARNENDU PAL
SWARNENDU PAL on 21 Jul 2021
technically these two things are same i think. Taking mean of mean and find out the whole mean of a multidimensional vector.

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