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How to find position of array

Asked by Wind flower on 17 Jun 2019
Latest activity Edited by madhan ravi
on 20 Jun 2019 at 15:19
For example i have data like this [11111100001111]
Now i need to find out the position of first 1 and last 1 of first group of 1s and then position of first 1 and last 1 of second group of 1s. How do i do this??
i have used' find' to find the position of all 1s but i dont want all...instead 1 want only the first and last position of groupof 1s

  2 Comments

[1 0 1 1 0 0 0 0 1 1 1 1] - the result would be?
for my data [11111100001111], the answer would be 1 and 6 for first set , 11 and 14 for the second set. Afer that i want to save that in array like this:
1 6
11 14

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2 Answers

Answer by Debasish Samal on 17 Jun 2019
Edited by Debasish Samal on 17 Jun 2019
 Accepted Answer

You can use regular expressions to do this.
x = '11111100001111';
expr = '1*';
[sInd,eInd] = regexp(x, expr)
This gives the following result:
sInd = 1×2
1 11
eInd = 1×2
6 14
You just need to convert the input data into a string.

  6 Comments

Wind flower: Did you see the answer below? I don’t know why my answer was marked Accepted mistakenly.
@Wind flower as far as I know xlsread returns a matrix of integers(if you are reading integers). So very basic approach would be using num2str to convert the num type to string type. Then iterate over each cell to get the result. I am not sure how your data looks like after reading it using xlsread. But I am sure you can figure out a way to optimise the conversion and get the desired result. Thanks.
@madhan ravi: Your answer was correct. Sorry first i got some error then i got to know. Your answer is simpler and correct. Sorry for the mistake
Thank You

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Answer by madhan ravi
on 17 Jun 2019

Simpler without any conversions:
s=[1 0 1 1 0 0 0 0 1 1 1 1]; % example data
x=s~=0;
Start = strfind([0,x],[0 1])
End = strfind([x,0],[1 0])

  3 Comments

s = 11111100001111; % if your data is indeed like below then
m = floor(log10(s));
D = mod(floor(s ./ 10 .^ (m:-1:0)), 10);
x=D~=0;
Start = strfind([0,x],[0 1])
End = strfind([x,0],[1 0])
Note that using numeric arrays as inputs to strfind is currently undocumented (and it even returns an error in GNU Octave). It would be nice if Mathworks changed the documentation. It would be even better if they extended this function to work on arrays of any object type.
@madhan ravi : Thank You

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