Thread Subject:

tricky logic situation

Dear MATLAB users,

I have a very tricky situation (at least it seems tricky to me).
I have a binary array, lets say,
a = [ 0 1 1 0 0 1 1 1 0 0 1 0 1 1 1 1 0 1 1 1 ]; (length = 20)
Now from this array I want to find the maximum number of 1s TOGETHER, not the number of 1s in the whole array (here maximum number of 1s is 13 but max. number of 1s TOGETHER is 4).
So, in this array 'a', the maximum number of 1s TOGETHER is 4 (i.e. from array elements 13 to 16). Position of 1s does not matter.

Thanks in advance!!
Jainam

On 6/18/2012 2:48 AM, Jainam wrote:
> Dear MATLAB users,
>
> I have a very tricky situation (at least it seems tricky to me).
> I have a binary array, lets say,
> a = [ 0 1 1 0 0 1 1 1 0 0 1 0 1 1 1 1 0 1 1 1 ]; (length = 20)
> Now from this array I want to find the maximum number of 1s TOGETHER,
>not the number of 1s in the whole array (here maximum number of 1s
>is 13 but max. number of 1s TOGETHER is 4).
> So, in this array 'a', the maximum number of 1s TOGETHER is
>4 (i.e. from array elements 13 to 16). Position of 1s does not matter.
>
> Thanks in advance!!
> Jainam
>

What is wrong with a simple loop?

-----------------------
a = [ 0 1 1 0 0 1 1 1 0 0 1 0 1 1 1 1 0 1 1 1 ];
N = length(a);
b = zeros(1,N);
b(1) = a(1);

for i = 2:N
     b(i) = a(i)*(a(i)+b(i-1));
end

[I,J]=max(b);
-----------------------

fprintf('starts at %d\n',J-I+1);
fprintf('ends at %d\n',J);

starts at 13
ends at 16

--Nasser

"Nasser M. Abbasi" <nma@12000.org> wrote in message <jrmr6d$8uh$1@speranza.aioe.org>...
> On 6/18/2012 2:48 AM, Jainam wrote:
> > Dear MATLAB users,
> >
> > I have a very tricky situation (at least it seems tricky to me).
> > I have a binary array, lets say,
> > a = [ 0 1 1 0 0 1 1 1 0 0 1 0 1 1 1 1 0 1 1 1 ]; (length = 20)
> > Now from this array I want to find the maximum number of 1s TOGETHER,
> >not the number of 1s in the whole array (here maximum number of 1s
> >is 13 but max. number of 1s TOGETHER is 4).
> > So, in this array 'a', the maximum number of 1s TOGETHER is
> >4 (i.e. from array elements 13 to 16). Position of 1s does not matter.
> >
> > Thanks in advance!!
> > Jainam
> >
>
> What is wrong with a simple loop?
>
> -----------------------
> a = [ 0 1 1 0 0 1 1 1 0 0 1 0 1 1 1 1 0 1 1 1 ];
> N = length(a);
> b = zeros(1,N);
> b(1) = a(1);
>
> for i = 2:N
> b(i) = a(i)*(a(i)+b(i-1));
> end
>
> [I,J]=max(b);
> -----------------------
>
> fprintf('starts at %d\n',J-I+1);
> fprintf('ends at %d\n',J);
>
> starts at 13
> ends at 16
>
> --Nasser

thanks a lot nasser!!
i was complicating the problem using while and switch but forgot the easy way..

On 6/18/2012 4:08 AM, Nasser M. Abbasi wrote:
> On 6/18/2012 2:48 AM, Jainam wrote:
>> Dear MATLAB users,
>>
>> I have a very tricky situation (at least it seems tricky to me).
>> I have a binary array, lets say,
>> a = [ 0 1 1 0 0 1 1 1 0 0 1 0 1 1 1 1 0 1 1 1 ]; (length = 20)
>> Now from this array I want to find the maximum number of 1s TOGETHER,
>> not the number of 1s in the whole array (here maximum number of 1s
>> is 13 but max. number of 1s TOGETHER is 4).
>> So, in this array 'a', the maximum number of 1s TOGETHER is
>> 4 (i.e. from array elements 13 to 16). Position of 1s does not matter.
>>
>> Thanks in advance!!
>> Jainam
>>
>


> What is wrong with a simple loop?
>
> -----------------------
> a = [ 0 1 1 0 0 1 1 1 0 0 1 0 1 1 1 1 0 1 1 1 ];
> N = length(a);
> b = zeros(1,N);
> b(1) = a(1);
>
> for i = 2:N
> b(i) = a(i)*(a(i)+b(i-1));
> end
>
> [I,J]=max(b);
> -----------------------
>
> fprintf('starts at %d\n',J-I+1);
> fprintf('ends at %d\n',J);
>
> starts at 13
> ends at 16
>
> --Nasser
>

If you just want the LENGTH of the longest 1's (and
not care where it starts or ends), you can
use this nice trick that I picked up from a post by Bruno
to this newsgroup

------------------------------
x = find(diff([0 a]) == 1);
y = find(diff([a 0]) == -1);
max(y-x+1)
--------------------------
ans =

      4

notice you need to do the [0 a] and [a 0] to get the
lengths right and have to check for 1 and -1 also.

see reference:

http://www.mathworks.com/matlabcentral/newsreader/view_thread/312417

--Nasser

"Nasser M. Abbasi" <nma@12000.org> wrote in message <jrmss6$de5$1@speranza.aioe.org>...
> On 6/18/2012 4:08 AM, Nasser M. Abbasi wrote:
> > On 6/18/2012 2:48 AM, Jainam wrote:
> >> Dear MATLAB users,
> >>
> >> I have a very tricky situation (at least it seems tricky to me).
> >> I have a binary array, lets say,
> >> a = [ 0 1 1 0 0 1 1 1 0 0 1 0 1 1 1 1 0 1 1 1 ]; (length = 20)
> >> Now from this array I want to find the maximum number of 1s TOGETHER,
> >> not the number of 1s in the whole array (here maximum number of 1s
> >> is 13 but max. number of 1s TOGETHER is 4).
> >> So, in this array 'a', the maximum number of 1s TOGETHER is
> >> 4 (i.e. from array elements 13 to 16). Position of 1s does not matter.
> >>
> >> Thanks in advance!!
> >> Jainam
> >>
> >
>
>
> > What is wrong with a simple loop?
> >
> > -----------------------
> > a = [ 0 1 1 0 0 1 1 1 0 0 1 0 1 1 1 1 0 1 1 1 ];
> > N = length(a);
> > b = zeros(1,N);
> > b(1) = a(1);
> >
> > for i = 2:N
> > b(i) = a(i)*(a(i)+b(i-1));
> > end
> >
> > [I,J]=max(b);
> > -----------------------
> >
> > fprintf('starts at %d\n',J-I+1);
> > fprintf('ends at %d\n',J);
> >
> > starts at 13
> > ends at 16
> >
> > --Nasser
> >
>
> If you just want the LENGTH of the longest 1's (and
> not care where it starts or ends), you can
> use this nice trick that I picked up from a post by Bruno
> to this newsgroup
>
> ------------------------------
> x = find(diff([0 a]) == 1);
> y = find(diff([a 0]) == -1);
> max(y-x+1)
> --------------------------
> ans =
>
> 4
>
> notice you need to do the [0 a] and [a 0] to get the
> lengths right and have to check for 1 and -1 also.
>
> see reference:
>
> http://www.mathworks.com/matlabcentral/newsreader/view_thread/312417
>
> --Nasser

ya, this approach is very smart too! thanks again nasser!!