How to count the numbers before consecutive negative values?

Question

Tawsif Mostafiz 2021-7-31

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/889557-how-to-count-the-numbers-before-consecutive-negative-values

评论： Tawsif Mostafiz 2021-7-31

Hi, I have a code, whose output is:

c =
0.4855   -0.1902   -0.1758    0.3935   -0.1264   -0.1274   -0.0914   -0.1149   -0.0930    0.5572    0.5098    1.0000    
0.9737    0.9508    0.9046    0.9083    0.8997

Now, I want to calculate the maximum number of consecutive negative numbers (in this case, it is, 5) and the number of values before it (in this case, it is 4). How do I do it?

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Tawsif Mostafiz 2021-7-31

Thanks!

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Answer 1

Image Analyst 2021-7-31

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https://ww2.mathworks.cn/matlabcentral/answers/889557-how-to-count-the-numbers-before-consecutive-negative-values#answer_757747

Try this:

mask = bwareafilt(c < 0, 1);
props = regionprops(mask, 'Area', 'PixelIdxList')
longestRun = props.Area % Will be 5
numbersBefore = props.PixelIdxList(1) - 1 % will be 4

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Answer 2

Walter Roberson 2021-7-31

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https://ww2.mathworks.cn/matlabcentral/answers/889557-how-to-count-the-numbers-before-consecutive-negative-values#answer_757727

c = [
0.4855   -0.1902   -0.1758    0.3935   -0.1264   -0.1274   -0.0914   -0.1149   -0.0930    0.5572    0.5098    1.0000    ...
0.9737    0.9508    0.9046    0.9083    0.8997]
c = 1×17
    0.4855   -0.1902   -0.1758    0.3935   -0.1264   -0.1274   -0.0914   -0.1149   -0.0930    0.5572    0.5098    1.0000    0.9737    0.9508    0.9046    0.9083    0.8997
mask = c < 0
mask = 1×17 logical array
   0   1   1   0   1   1   1   1   1   0   0   0   0   0   0   0   0
starts = strfind([0 mask], [0 1 1])
starts = 1×2
     2     5
stops = strfind([mask 0], [1 1 0]) + 1
stops = 1×2
     3     9
runlengths = stops - starts + 1
runlengths = 1×2
     2     5
[maxrunlength, idx] = max(runlengths)
maxrunlength = 5
idx = 2
num_items_before_run = starts(idx) - 1
num_items_before_run = 4