Getting distance between specific numbers in array after using diff() function

I would like to find a distance between specific arrays (this distance represents time), I got it as an output of using diff function thanks to it I know when foot movement started. For example let's say I have array like this:

x = [ 0     1     0     0     0     0     0     0     0     0     0     0    -1     0     0     0     1    0   0   0  -1]

And I would like to automate the code and find the distance - how many zeros are between 1 and -1 (i don't want from -1 and 1), So for example from this code I'd know that I have 1) 10 zeros space between first 1 and -1 and index range between first and last zero, and for the 2) 3 zeros space and also indexes. Is that possible to do?

Answer 1

[Jan]

x =  [0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1, 0, 0, 0, 1, 0, 0, 0, -1];

pos = find(x ==  1);
neg = find(x == -1);
len = neg - pos - 1

len = 1×2

10 3

If the trailing -1 is missing:

len = neg(1:numel(pos)) - pos - 1;

[M]

thanks, but how get an index range for this numbers in len?

[Jan]

What is an "index range"? Please post exactly, which output you need.

[Image Analyst]

I assume it's like in my answer below where I give the starting and ending index for each run of zeros.

[Jan]

Thanks. So starting is at pos+1 and ending at neg-1.

[Image Analyst]

x =  [0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1, 0, 0, 0, 1, 0, 0, 0, -1];
pos = find(x ==  1);
neg = find(x == -1);
len = neg - pos - 1

len = 1×2

10 3

% Find out where each run of 0's start and end>
startingPositions = pos + 1

startingPositions = 1×2

3 18

endingPositions = neg - 1

endingPositions = 1×2

12 20

It seems to miss the zero starting and ending at index 1, and the run starting at 14 and ending at 16.

Maybe search for the zeros directly instead of for 1 and -1.

Answer 2

[Image Analyst]

If you have the Image Processing Toolbox you can use regionprops to find the location of the "0" regions:

x = [ 0     1     0     0     0     0     0     0     0     0     0     0    -1     0     0     0     1    0   0   0  -1];
props = regionprops(x == 0, 'Area', 'PixelIdxList');
allZeroLengths = [props.Area]

allZeroLengths = 1×4

1 10 3 3

for k = 1 : numel(props)
    startingIndexes(k) = props(k).PixelIdxList(1);
    endingIndexes(k) = props(k).PixelIdxList(end);
end
startingIndexes % Show in command window

startingIndexes = 1×4

1 3 14 18

endingIndexes

endingIndexes = 1×4

1 12 16 20