how to implement a moving window with a condition ?

I have an row vector 1x10000. this is a representation of series of spikes with its magnitudes being normalized(maximum amplitude 1) . My aim is to find out number of spikes within every 100 samples. I have defined a spike if the magnitude of spike crosses 0.7 or else neglected. First I should take 1st 100 samples and check for number of spikes. Then I should take samples from 2 to 101 and do the same. Then choose samples from 3 to 102 and repeat this till the sample reaches 10000. How can I implement this.

Answer 1

[Guillaume]

You can either use conv (i.e. a convolution) to compute a count of something over a sliding window, or since R2016a, movsum:

% FAKE DATA
x         = rand(1000,1)

% PARAMETERS
window    = 100
threshold = 0.7

%no-loop code:
abovethreshold = x >= threshold;

%with conv:
windowcount = conv(abovethreshold, ones(window, 1), 'valid'); 

%with movsum:
windowcount = movsum(abovethreshold, window, 'Endpoints', 'discard');

Answer 2

[Pawel Jastrzebski]

Consider the following code:

% FAKE DATA
x         = rand(100,1)

% PARAMETERS
window    = 50
threshold = 0.7
LoopCntr  = length(x)-window+1

% PREALLOCATION
m         = zeros(LoopCntr, window); % moving range
PksCntr   = zeros(LoopCntr,1); % peak conter
RowNames  = cell(1, LoopCntr); % row names for the table
ColNames  = cell(1,window)   ; % column names for the table   

for i = 1:LoopCntr

      % get your values for the moving range into a matrix
      m(i,:)      = x(i:i+window-1);
      % check them for the conditions and count the peaks
      PksCntr(i)  = nnz(m(i,:)>threshold)
      % get the names for rows and columns
      RowNames(i) = {[num2str(i) '-' num2str(i+window-1)]};
      ColNames(i) = {['V' num2str(i)]}
  end

ColNames(end)                 = {'NoOfPeaks'};

% Convert matrixec to the table
tVal                          = array2table([m PksCntr]);
% add names to columns and rows
tVal.Properties.VariableNames = ColNames;
tVal.Properties.RowNames      = RowNames;

Remarks:

• I'm not sure but chances are you can achieve the same thing without a loop
• Variables window and theshold might me the reserved words if you have any toolboxes installed (not sure)
• Storing everything in the table at the of the code is not necessary but it helps keep the data organised

[Guillaume]

"I'm not sure but chances are you can achieve the same thing without a loop"

Of course, it can be done without a loop.