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# finding the mean for large data

Asked by FIR on 30 Nov 2012

I have 3 rows ans 192 column,i want to find mean for each 9 columns in row wise,

for ex if i have rand(3,192)

taking 3x9 , i need mean in row wise so i will have 3x1 matrix after finding mean

for each 3x9 i want to perform

Jos (10584) on 30 Nov 2012

192 is not divisible by 9, so what to do with the last columns?

Image Analyst on 30 Nov 2012

It's not "large" either. Before I read it I thought that he was talking hundreds of millions of elements, not five hundred and something. (And there is a "bug" for the case of calculating the mean for large numbers of singles)

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Answer by Andrei Bobrov on 30 Nov 2012
Edited by Andrei Bobrov on 30 Nov 2012
```A = rand(3,192);
n = 9;
```
```s = size(A);
out = squeeze(nanmean(reshape([A nan(s(1),mod(-s(2),n))],s(1),n,[]),2));
```

or

```out = blockproc(A,[1 n],@(x)mean(x.data));
```

or

```k = s(2) - rem(s(2),n);
out = [squeeze(mean( reshape(A(:,1:k),s(1),[]),2 )) , mean(A(:,k+1:end),2)];
```

```A = rand(3, 192);