Hello all.

I have a column of data of several hundred elements long consisting of 1s and 4s, like this e.g.;

a = 1
4
4
4
4
1
1
4
1
4
....

I need to obtain the total frequency for the appearance of several sequences of combinations of 1 and 4, i.e. how many times do sequences "1, 4", "1, 1, 4", "1, 1, 1, 4", and so on, appear in the column.

Any suggestions? Thanks in advance.
Iain

Hi, if the sequences that you want to check is finite try this; you can get other ideas from it good luck:
a=[
4
4
4
4
1
1
4
1
4];
count=0;
for i=3:size(a);
    if a(i-2:i)==[1,1,4]';
        count=count+1;
    end 
end 
% the "count" value now has the frequency of [1 1 4]' in a

Iain:
I don't think you really want to do this.  Think about it.  There are
millions of different possible patterns of a variety of different
lengths from 2 to N (the number of elements).  I don't think you'd
really want them all even if you could get them from some brute force
algorithm (which is possible though).  If you could narrow it down to
a finite number of predefined sequences then you could do it.  For
example you want sequences of only up to 5 digits long.  You could
then use filter or imfilter with the pattern you're looking for and
then look for a particular value, i.e. sum(pattern .* pattern), in the
filtered output.

stu <tmnarges2@live.utm.my> wrote in message <895557605.43596.1296825277597.JavaMail.root@gallium.mathforum.org>...
> Hi, if the sequences that you want to check is finite try this; you can get other ideas from it good luck:
> a=[
> 4
> 4
> 4
> 4
> 1
> 1
> 4
> 1
> 4];
> count=0;
> for i=3:size(a);
>     if a(i-2:i)==[1,1,4]';
>         count=count+1;
>     end 
> end 
> % the "count" value now has the frequency of [1 1 4]' in a

Thanks for these suggestions. 

Apologies ImageAnalyst for lack of clarity in original post, I didn't mean to imply 2 to N sequence patterns - the max length of sequence will likely be around 10.  

stu - that idea is working very well (so far!), many thanks.

"Iain" wrote in message <iignu3$qg$1@fred.mathworks.com>...
> Hello all.
> 
> I have a column of data of several hundred elements long consisting of 1s and 4s, like this e.g.;
> 
> a = 1
> 4
> 4
> 4
> 4
> 1
> 1
> 4
> 1
> 4
> ...
> 
> I need to obtain the total frequency for the appearance of several sequences of combinations of 1 and 4, i.e. how many times do sequences "1, 4", "1, 1, 4", "1, 1, 1, 4", and so on, appear in the column.
> 
> Any suggestions? Thanks in advance.
> Iain


Take a look at STRFIND and CELLFUN

C = [1 1 4 1 1 4 1 1  4 1 4 4 4 1 4 1 4 1 1].' ; % column vector
seq = {[1 4 1],[1 4],[4 1 1 4],[9 9 9]} % sequences
N = cellfun(@(x) numel(strfind(C(:).',x(:).')), seq) 

Note that strfind requires row vectors.

hth
Jos