MATLAB: Find max value in each interval of array data?

Question

I have an array which stored samples of a signal during a period of time which called signalArray(1:n) and n is number of samples.

I'm going to split signal samples to several time-segments e.g. M segments (0:n/M), (n/M+1:2n/M+1),.... and I want to find maximum value of signal in each of theses M segments.

Are there any efficient methods for this?

Then your poblem is not well defined. Do you simply want a final, shorter segment of which you also compute the maximum? — Luis Mendo
– Luis Mendo, Commented Jul 30, 2017 at 15:52
Sure, it can be done. Do you need to specify M as the number of segments (including the last, possibly shorter segment), or as the segment length (except for the possibly shorter last segment)? — Luis Mendo
– Luis Mendo, Commented Jul 30, 2017 at 15:56

Luis Mendo · Accepted Answer · 2017-07-30 16:30:15Z

2

If M were assured to divide n you would only need to reshape the data into an M-row matrix, to trasnform each segment into a column, and then take the maximum of each column.

In general, if M doesn't necessarily divide n, the same procedure can be applied but the the last segment (i.e. column) may need to be padded with NaN entries. This works because max ignores NaN values.

n = 21;                   % Data size
M = 4;                    % Number of segments. If M doesn't divide n, the last 
                          % segment will be shorter (and will be padded by NaN)
signalArray = rand(1,n);  % Example data
t = NaN(ceil(n/M), M);    % Define matrix of NaN's with required size
t(1:n) = signalArray;     % Fill data (in column-major order). Some entries
                          % in the last column may be left as NaN
result = max(t, [] ,1);   % Maximum of each column

edited Jul 30, 2017 at 16:30

answered Jul 30, 2017 at 15:38

Luis Mendo

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