maximum of elements

Hello,

I have a dataset 'a' with 2000 rows and 1 column. I want to create a new dataset 'b' which contains values that are the maximum of the 10 previous rows of 'a'. So row 11 of dataset 'b' has to contain the maximum value of rows 1-10 of dataset 'a' How can I program this?

Thanks, Pieter

Answer 1

[Arnaud Miege]

There may be a cleaner way of doing this the following should work:

b = zeros(size(a));
b(1:10) = a(1:10);
for k=11:length(a)
    b(k) = max(a(k-10:k-1));
end

HTH,

Arnaud

[Pieter]

Thanks!

Exactly what I was searching for!

Pieter

Answer 2

[Jan]

NLFILTER of Matlab's Image Processing Toolbox can calculate the moving max:

fun = @(x) max(x(:));
b = nlfilter(a, [10, 1], fun);

Do you have the Image Processing Toolbox?

[Jan]

Do not use this! It is more than 1000 times slower than the BUFFER method of my other answer.

Answer 3

[Jan]

If your input is not too large (2000 is no problem), you can expand the data using BUFFER. This is 1300 times faster than NLFILTER and much faster than the loop:

M = max(buffer(a, 10, 9, 'nodelay'))
M = M(:);  % BUFFER replies a row vector
b = [a(1:10); M(1:end - 1)];