How to calculate the number of consecutive negative values in an array before a positive appears?

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Tawsif Mostafiz 2021-7-29

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评论： Image Analyst 2021-7-30

I am writing a code, where the output is as follows:

c =
-0.4607   -0.4659   -0.5165   -0.5168   -0.5164   -0.4626   -0.4668   -0.3730   -0.3426    0.3224 
0.3251    0.3270    0.3281    0.3400   -0.1816   -0.1830   -0.1851     1

I want to calculate the number of negative values before a positive value appeares for each cases. How do I do that?

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Answer 1

Image Analyst 2021-7-29

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Here's another way:

c =[-0.4607   -0.4659   -0.5165   -0.5168   -0.5164   -0.4626   -0.4668   -0.3730   -0.3426    0.3224 ...
0.3251    0.3270    0.3281    0.3400   -0.1816   -0.1830   -0.1851     1]
props = regionprops(c<0, 'Area'); % Measure lengths of all runs of negative values.
results = [props.Area] % [9, 3] % Turn from structure into a vector.

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Tawsif Mostafiz 2021-7-30

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Thanks everyone! I have another problem. Suppose the output is like this:

results =
     1    14     3    14

Now suppose I want to find the count of numbers (both positive and negative) before the maximum count of negative numbers appears. As the maximum 14 comes twice and I need the first instance, I am calculcating the maximum by this:

maximum=max(results);
location=find(results==maximum,1);

Now, how do I calculate, how many numbers appear before it?

Image Analyst 2021-7-30

That number is simply the location minus 1. So it finds 14 at location 2 for the max, and there is one number, 1, before that location.

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Answer 2

Adam Danz 2021-7-29

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c = [-0.4607   -0.4659   -0.5165   -0.5168   -0.5164   -0.4626   -0.4668   -0.3730   -0.3426    0.3224 ,...
0.3251    0.3270    0.3281    0.3400   -0.1816   -0.1830   -0.1851     1];
A = c(:)<0;
B = diff(find([0,A(:).',0]==0))-1; 
B(B==0) = []
B = 1×2
     9     3