# I want to calculate the RMS, MEAN, STD of the first three elements of any predefine array and store it in new array and then calculate the same for the next three elements

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Rajeev Kumar on 9 Jun 2022
Edited: dpb on 10 Jun 2022
I want to calculate the RMS, MEAN, STD of the first three elements of any predefine array and store it in new array and then calculate the same for the next three elements and store it in the same new array and so on till last.

dpb on 9 Jun 2022
Edited: dpb on 9 Jun 2022
N=size(x,1); % number rows in x
g=kron([1:N/3].',ones(3,1)); % grouping variable by three
[gmean,gstd,grms]=grpstats(x,g,{'mean','std',@rms})); % compute
See grpstats for all the details of possible ways to organize output.
NB: the above requires N be an even multiple of 3
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dpb on 10 Jun 2022
Edited: dpb on 10 Jun 2022
Use "the MATLAB way" I showed you instead.
"x" is your "predefined array"; simply use your variable name. You'll want to add error checking or otherwise handle the case of other than a multiple of three records if it is ever possible that condition can arise; we don't have sufficient information to know about edge case.
You can use/rearrange the returned statistics arrays with whatever variable structure/names you wish for the end result, but compute the results efficiently with grouping a variable.
mean=std(B);
Don't use mean as a variable; it's the builtin function for the statistic; doing this will create all sorts of unexpected havoc.

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