Extract and average from matrix

Hello all, Im trying to extract every 7 rows of a matrix and average them (mean). As an example:

4.20
4.10
4.10
4
3.90
3.80
NaN
3.80
3.90
3.90
3.70
3.60
3.60
3.40
3.40
3.30
3.30
3.30
3.30
3.10
3.10

What code would i need to take the first 7 rows and average them, and to continually do this for the matrix i.e. average of rows 1:7 8:14 15:21

Thanks in advance.

Answer 1

[Bob Thompson]

The lowest difficulty way of doing this, that I can think of, is to use a for loop.

for i = 1:length(data)/7;
    ave(i) = mean(data(7*(i-1)+1:i*7));
end

If you're looking for a non-loop method you might try using reshape first, and then average each column.

data2 = reshape(data,7,[]);
ave = mean(data2);

[Joseff Saunders]

Brilliant, thank you

[Image Analyst]

The second method (same as my answer below) is clever if you've never seen it before.

We see this question (and the answer) all the time - I guess I should add it to the FAQ.

EDIT: OK, I've added it to the FAQ: How do I compute the mean of a vector in blocks?

Answer 2

[Image Analyst]

Try reshape()

vec = (1 : 70)' % Sample data
m2d = reshape(vec, 7, [])
means7 = mean(m2d, 1)