How to find position of something

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Martina
Martina il 7 Dic 2013
Risposto: Roger Stafford il 7 Dic 2013
Hi, I am having a problem with part of my homework. I have a column with numbers and NaN-s. If I have 5 or more NaN-s in a row I need to know place/position where NaN start (j) and end (i) ( in all column). For example 7 6 5 NaN NaN NaN NaN NaN NaN 9 7
j=4 i=9 Thanks you very much :)

Risposta accettata

Roger Stafford
Roger Stafford il 7 Dic 2013
You can use the 'find' and 'diff' functions as well as 'isnan' to accomplish that. Let A be your column vector of elements with possible NaNs among them.
m = 5; % The minimum length of consecutive NaNs to record
f = find(diff([false;isnan(A);false]));
B = [f(1:2:end-1),f(2:2:end)-1]; % Get all start and end indices for NaN consecutive sequences
B = B(B(:,2)-B(:,1)+1>=m,:); % Eliminate all with fewer than m NaNs
The first column of array B contains the start indices and the second column the end indices for consecutive sequences of at least five NaNs.

Più risposte (2)

Mohammad Monfared
Mohammad Monfared il 7 Dic 2013
Suppose you have a column or row vector named 'A',
find(isnan(A))
  4 Commenti
Martina
Martina il 7 Dic 2013
But I have lot of groups :(
Mohammad Monfared
Mohammad Monfared il 7 Dic 2013
It's not a straightforward simple line job, to me. One trick is to use the diff(isnan(A)) to find the boundaries of NaN groups and one more 'diff' to get the length of each group. Then a loop might be used afterward. Think about it (since it is a homework ;) ) a bit. If no success, I'll give the answer.

Accedi per commentare.


Image Analyst
Image Analyst il 7 Dic 2013
Modificato: Image Analyst il 7 Dic 2013
Really easy if you have the Image Processing Toolbox. Do you have that?
measurements = regionprops(isnan(vector), 'PixelIdx');
% just 2 or 3 lines more and you've got it.
By the way, you shoudl have tagged it as homework - I did this for you this time.

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