MATLAB: How to fill a column with 1’s between two specific values and with 0 otherwise

matrix manipulation

Dear all
I have a matrix with 27 columns. The rows are time periods. Each column takes value 1, 0 or -1. For instance, a typical column would look like this:
 % 
0
0
1
0
0
0
-1
0
0
1
0
0
0
0
-1
0
0
1
end
If you imagine a time series, values of 1 mean a peak, values of -1 mean a trough. Hence, we can define a period of expansion as the period between any t=1 and t=-1 (including these two endpoints).
I want to create a matrix such that each column has 1's in every period belonging to an expansion period and 0's otherwise. For instance, the column above would become
 %

0
0
1
1
1
1
1
0
0
1
1
1
1
1
1
0
0
0
end
My question is how to this in an efficient manner and in a way that applies to every column of the matrix at once. I struggling with the end values. For instance, the last value is a 1 but since there is no -1 after it, it should become a 0!
Thanks for your help
James
Edit: Btw, this is what I have so far…. it has been running for quite a while so I have no idea whether it works or not.. but even if it does it really is inefficient
 %
 [R, C] = size(mBBpre); %mBBpre is the matrix of 0's,1's and -1's
 mExpansionPre = NaN(R,C);        %this is where I want to put the values                                          
 for j = 1 : C
 % iLocalPeak is the number of Peaks for column j    
 iLocalPeak = vPeaksPre(j,1);            
 % iLocalTrough is the number of Troughs for column j
 iLocalTrough = vTroughPre(j,1);             
 % Pre-allocates space                               
 vPositionPeaksPre = NaN(iLocalPeak,1);     
 % Pre-allocates space                                 
 vPositionTroughPre = NaN(iLocalTrough,1);                               
 % Stores Positions of Peaks
 vPositionPeaksPre = find(mBBpre(:,j) == 1); 
 % Stores Positions of Troughs                            
 vPositionTroughPre = find(mBBpre(:,j) == -1);                               
 for k = 1 : numel(vPositionPeaksPre)
    for i = 1 : numel(mExpansionPre)
        if i >= vPositionPeaksPre(k,1) && i <= vPositionTroughPre(k,1)
           mExpansionPre(i,j) = 1;
        else
            mExpansionPre(i,j) = 0;
        end
    end
 end
 end
 end

Best Answer

Sometimes it's just simpler to loop...
i1=find(v==1);  % start
i2=find(v==-1); % end
if length(i2)>length(i1)  % end effect, if any
  v(i2(end))=0;           % zero that position
  ix(end)=[];             % and cleanup array length
end
for i=1:length(i1)        % fill in the array locations wanted
  v(i1(i):i2(i))=ones(i1(i)-i2(i)+1,1);
end
Some effort could turn this into an arrayfun candidate no doubt, but I suspect the above will be just as fast and easier to debug/maintain...
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