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

Question

M 2022-6-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1738895-getting-distance-between-specific-numbers-in-array-after-using-diff-function

评论： Image Analyst 2022-6-14

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?

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Answer 1

Jan 2022-6-12

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https://ww2.mathworks.cn/matlabcentral/answers/1738895-getting-distance-between-specific-numbers-in-array-after-using-diff-function#answer_984015

编辑：Jan 2022-6-12

在 MATLAB Online 中打开

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;

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Jan 2022-6-14

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

Image Analyst 2022-6-14

在 MATLAB Online 中打开

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.

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Answer 2

Image Analyst 2022-6-12

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1738895-getting-distance-between-specific-numbers-in-array-after-using-diff-function#answer_984045

编辑：Image Analyst 2022-6-13

在 MATLAB Online 中打开

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