Index Subset of Array in For Loop in MATLAB

Question

I have a question regarding indexing and loops in MATLAB. I have a vector of length n (named data in the code below). I want to examine this vector 4 elements at a time inside of a for loop. How can I do this? My attempt included below does not work because it will exceed the array dimensions at the end of the loop.

for k = 1:length(data)

    index = k:k+3;

    cur_data = data(index);

    pre_q_data1 = cur_data(1);
    pre_q_data2 = cur_data(2);
    % Interweaving the data
    q = [pre_q_data1; pre_q_data2];
    qdata = q(:)';


    pre_i_data1 = cur_data(3);
    pre_i_data2 = cur_data(4);

    i = [pre_i_data1; pre_i_data2];
    idata = i(:)';

end

You need to stop when k+3 is equal to the last index of the array, not when it's equal to end+3. — beaker
– beaker, Commented May 17, 2017 at 15:00
Also you can get rid of the for-loop and use buffer instead. See here. — kedarps
– kedarps, Commented May 17, 2017 at 15:48
@kedarps, * "Also you can [...] use buffer instead if you have the signal processing toolbox" — Wolfie
– Wolfie, Commented May 17, 2017 at 15:54

Wolfie · Accepted Answer · 2017-05-17 15:58:43Z

0

You shouldn't have k go all the way to length(data) if you're planning on indexing up to k+3.

I've also taken the liberty of greatly simplifying your code, but feel free to ignore that!

for k = 1:length(data)-3
    % maximum k = length(data)-3, so maximum index = length(data)-3+3=length(data)
    index = k:k+3;
    cur_data = data(k:k+3);
    % Interweaving the data
    q = cur_data(1:2); % transpose at end of line here if need be
    i = cur_data(3:4); % could just use data(k+2:k+3) and not use cur_data
end

edited May 17, 2017 at 15:58

answered May 17, 2017 at 15:53

Wolfie

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1 Comment

Aaron Over a year ago

Thanks a lot... Sometimes the simplest solutions fly right over your head.

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