How to find the maximum after every 5 rows in a matrix?

Hi all, I have a matrix of size 525600x23 and I would like to find the maximum value after every 5 rows, so that my output matrix will have the size 105120x23.

I used the following code (because it worked with finding the Mean) but the output dimension for this case gave me 5x105120x23. However I wish to actually get 105120x23 size only.

Answer = squeeze(nanmax(reshape(Mymatrix,[5,105120,23]),1));

Any help is appreciated.

Thank you!

Answer 1

[dpb]

nGrp=5;            % grouping size
mx=reshape(nanmax(reshape(x,nGrp,[])),size(x,1)/nGrp,[]);

The key is to remember storage order is column major. Try the following at the command line to visualize...

x=rand(8,3);
nGrp=2;

Now apply the above and look at x and mx. If you still don't follow the reason it works, break down the expression and do the two pieces individually looking at the result of each step.

[B.kun]

Thank you for your answer. However, when I tried it, it gave me 23x105120 dimension... I tried adjusting the numbers and rearrange something from your code but none of the ways seem right...

[B.kun]

Ah, no worries! I reshaped your code once again and I got what I wanted.

mmx = reshape(mx,105120,23);

Thank you.

[dpb]

The key to these kinds of problems is to work on small subsets you can visualize at the command line...

Sorry, I was typing at the command line and missed the divisor to get the number of rows divided by the grouping constant...and was thinking of the transposed x instead of original, too. Edited Answer as well.

mx=reshape(nanmax(reshape(x,nGrp,[])),size(x,1)/nGrp,[]);