MATLAB: How to find start and end points of non-zero elements in a vector

find

I have some vectors with mostly zeros and a few non-zero values all grouped together (see example plot). I want to know the index for the start and end points of these non-zero areas, i.e. the start and end of the peaks on the plot.

I can use find to get the non-zero areas, then iterate through with a loop to find everywhere the jump in values is greater than 1, but is there a better way to do this?

Best Answer

t = YourVec ~= 0;
findstr([0 t], [0 1])-1  %gives indices of beginning of groups
findstr([t 0], [1 0])    %gives indices of end of groups

Related Solutions

MATLAB: Clusterization of data in 1-D vector

There are lots of alternatives.

Input A is a vector of 1s and 0s.
n is minimum number of 0s between 1s separate groups of 1s.
T is a table showing the start and stop index for each consecutive group of 1s split by less than n zeros and the length of each group.

A = [0 0 0 1 1 1 0 0 1 1 1 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 0 1 1 0 1 0 1 1 0 1 0 0 0 0 1 1 1 1];
% Length of each group of consecutive 1s
T = table();
T.OnesLength = diff(find([0;A(:);0]==0))-1;
T(T.OnesLength==0,:) = []; 
% Index of 1st '1' in each group of consecutive 1s
T.OnesStart = find(diff([0;A(:)])==1);
% Index of last '1' in each group of consecutive 1s
T.OnesStop = T.OnesStart + T.OnesLength - 1; 
% Determine the number of 0s between consecutive 1s
ZerosBetween = [T.OnesStart(2:end) - T.OnesStop(1:end-1); NaN]-1;
disp(T)
    OnesLength    OnesStart    OnesStop
    __________    _________    ________

        3             4            6   
        3             9           11   
        6            18           23   
        2            29           30   
        1            32           32   
        2            34           35   
        1            37           37   
        4            42           45   
% join groups of consecutive 1s with less than n zeros between. 
n = 3; 
joinGroups = ZerosBetween < n;
t = find(diff([0;joinGroups])==1);
f = find(diff([0;joinGroups])==-1);
T.remove = false(height(T),1); 
for i = 1:numel(t)
    T.OnesStop(t(i)) = T.OnesStop(f(i));
    T.OnesLength(t(i)) = sum(T.OnesLength(t(i):f(i))) + sum(ZerosBetween(t(i):f(i)-1));  
    T.remove(t(i)+1:f(i)) = true; 
end
T(T.remove,:) = []; 
T.remove = [];
disp(T)
    OnesLength    OnesStart    OnesStop
    __________    _________    ________

        8             4           11   
        6            18           23   
        9            29           37   
        4            42           45

Now you can use the segment length and the start/stop indices to compute the segement centers.

MATLAB: How to find the elements in a matrix that follow a certain pattern

This seems to work in the data you presented:

v = [0;
     0;
     0
     5 
     6
     7
     8
     0 
     0 
     0
     12
     13
     0
     0];
nzi = diff([0; v]);
nzigt0 = find(nzi > 1);
nzilt0 = find(nzi < 0);
Output = [v(nzigt0)  v(nzilt0-1)]
Output =
       5     8
      12    13

Best Answer

Related Solutions

MATLAB: Clusterization of data in 1-D vector

MATLAB: How to find the elements in a matrix that follow a certain pattern

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