list the result of the index values in ranges

Hello,

I have an array that is populated with the values 1,2 or 3.

   a = [1 1 2 2 3 3 2 2 1 1];

and I want to list the ranges of each value. The find function retrieves the index to each number which is great.

   [col1] = find(a==1)
   [col2] = find(a==2)
   [col3] = find(a==3)

but is there a function or some logic i can use to list col1, col2, and col3 as ranges? as in col1 = 1-2 and 9-10 and col2 = 3-4 and 7-8 etc etc.

I appreciate any ideas or help.

Thank you in advance!

[Jos (10584)]

You might want to search for run length encoding.

Answer 1

[Jos (10584)]

A = [1 1 2 2 3 3 2 2 1 1];
X = arrayfun(@(k) find(A==k),1:3,'un',0) ;
Y = cellfun(@(v) [v([true diff(v) > 1]) ; v([diff(v) > 1 true])]', X,'un',0) ;
% Y{k} contains the start indices (1st column) and end indices (2nd column) for a sequence of the value k in A

[Nasser Ramsis]

Thank you.

This is working great in 1 of my functions but this other function is giving me this message:

Index exceeds matrix dimensions.

Error in @(v)[v([true,diff(v)>1]);v([diff(v)>1,true])]'

Error in test (line 60) Y = cellfun(@(v) [v([true diff(v) > 1]) ; v([diff(v) > 1 true])]', X,'un',0) ;

Any ideas? do you want to see the entire code?

Answer 2

[Andrei Bobrov]

a = [1 1 2 2 3 3 3 2 2 1 1];

l = diff([0,a(:)'])~=0;
b = [strfind(l,[1 0]);strfind([l,1],[0 1])]';
out = accumarray(a(l)',1:size(b,1),[],@(x){sortrows(b(x,:))});