# confusion during finding out the mean of a 3d vector

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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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SWARNENDU PAL on 21 Jul 2021
Thanks for your reponse sir. But i got different. I dont know what is the problem. Is there any probable reason for this?
Bruno Luong on 21 Jul 2021

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
Bruno Luong on 21 Jul 2021
. Then which one should be used?
A=[0 1; NaN 1; NaN 1; NaN 1; NaN 1; NaN 1; NaN 1; NaN 1; NaN 1]
A = 9×2
0 1 NaN 1 NaN 1 NaN 1 NaN 1 NaN 1 NaN 1 NaN 1 NaN 1
mean(mean(A,'omitnan'),'omitnan')
ans = 0.5000
mean(mean(A,'all','omitnan'))
ans = 0.9000
SWARNENDU PAL on 21 Jul 2021
I think 2nd one is the correct and more meaningful as it gives the mean of all numbers.

Jonas on 21 Jul 2021
your second approach takes mean values of means and the first approach takes the mean value of all elements
Walter Roberson on 21 Jul 2021
Those work out the same except when there are nan that are being omitted.
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.