# 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

3 views (last 30 days)

Show older comments

##### 0 Comments

### Answers (1)

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

NB: the above requires N be an even multiple of 3

##### 2 Comments

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.

### See Also

### Categories

### Products

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!