Detecting length and number of occurrences in a logical array

EX:

array1 = [0 0 0 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 1 1 1 1 0 0 0 1]

I want to extract the number of times of consecutive 1's in a separate array eg: array2 = [4 2 6 1], where the length of array 2 is equal to the amount of groups of consecutive 1s and the values is the length of the chain of 1s. I also want to ensure that at 1's at the beginning and end of the arrays are captured.

Answer 1

[the cyclist]

Download Jan's RunLength utility from the File Exchange. It will do exactly what you want.

array1 = [0 0 0 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 1 1 1 1 0 0 0 1];
[b n] = RunLength(array1);
array2 = n(b==1)

array2 =

     4     2     6     1

[Jason MacNaughton]

Thank you!

Answer 2

[Image Analyst]

Jason, if you want a simple way to do it using built-in Mathworks functions and without using some third party File Exchange submission, and if you have the Image Processing Toolbox, you can simply use regionprops(). Here's an example:

array1 = [0 0 0 0 0 1 1 1 1 0 0 1 1 0 0 0 0 1 1 1 1 1 1 0 0 0 1]
props = regionprops(logical(array1), 'Area')
allLengths = [props.Area]

regionprops() labels each contiguous run of 1's and then measures each run and puts the results into a structure array.

props =

4×1 struct array with fields:

Area

Using the bracket trick in the third line concatenates all Area fields from the structure into one single vector.

allLengths =

4 2 6 1

[Andrei Bobrov]

+1

Answer 3

[Andrei Bobrov]

Without Toolboxes and Fileexchanges

a = accumarray(cumsum([0;diff(array1(:))] == 1).*array1(:)+1,1);
out = a(2:end);

[Amanda Beatty]

Thank you, very helpful! Your code only accurately determined the first run length for me (if the array starts with a 1) when you add a 0 to the array and then diff(), not the other way around.

a = accumarray(cumsum(diff([0;array1(:)]) == 1).*array1(:)+1,1);
out = a(2:end);

[Image Analyst]

@Amanda Beatty what was your array? Did you try my answer above that uses regionprops?

[Amanda Beatty]

@Image Analyst I don't have the image processing toolbox so I couldn't use regionprops. My array was array1 = [1 1 1 1 0].

%original
a = accumarray(cumsum([0;diff(array1(:))] == 1).*array1(:)+1,1);
out = a(2:end)

out =

  1×0 empty double row vector
  
%my edit  
a = accumarray(cumsum(diff([0;array1(:)]) == 1).*array1(:)+1,1);
out = a(2:end)

out =

     4

I don't know, maybe I just had a typo or something that haven't noticed yet, but in the end it did the job, so that's what matters :)

[Image Analyst]

Maybe try findgroups