Create index between values

Hi,

I have a 5 x 1 array, a = [ 0 1 0 2 0]. (this is a generalization of a larger problem)

I want create and index that fills all the values starting with 1, and ending at the last occurance of the number 2 (that does not have another 1 in between)?

I want to create b = [0 1 1 1 0].

I can do:

 b = zeros(1,length(a))
 b(strfind(a, [1]):strfind(a, [2])) = 1

That works for that specific case.

But, what if I have a = [ 0 1 0 2 0 2 1]? I want to create b = [0 1 1 1 1 1 0].

Any help woudl be appreciated! Thanks!

Inna

Answer 1

[per isakson]

Study this

%%
a = [0,1,0,2,0,2,1];
ixb = find( a==1, 1,'first'); % begin
ixe = find( a==2, 1,'last');  % end
%%
b = zeros(size(a));
b(ixb:ixe)=1;

b contains the result

>> b
b =
     0     1     1     1     1     1     0

[Inna Pelloso]

Thank you, I didn't know about the 'first' and 'last' option.

What if I have multiple such sequances within a, and want to index them? For example,

a = [0,1,0,2,0,2,1,0,1,0, 2 ], 

and I want

b = [0, 1, 1, 1, 1, 1, 0, 1, 1,1]

[per isakson]

"the 'first' and 'last'" using Matlab includes a lot of searching and reading of the documentation.

[per isakson]

%%
a = [0,1,0,2,0,2,1,0,1,0,2];
chr = sprintf('%d',a);
[ix1,ix2] = regexp( chr, '1[^1]+2', 'start', 'end' );
%%
b = zeros(size(a));
for jj = 1 : numel(ix1)
    b(ix1(jj):ix2(jj)) = 1;
end

and inspect b

>> b
b =
     0     1     1     1     1     1     0     0     1     1     1
                                         ^

I think there is a mistake in your value of b ; a missing zero.

regexp() requires more than searching and reading the documentation.

Answer 2

[Inna Pelloso]

Thank you! Really appreciate it.