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From: fckool on 3 May 2010 09:03
hi.. I have this code, and i want optimize it.. any suggestion?

thank you in advance.


clear all;
File=input('Ficheiro: ','s');
fid=fopen(File,'rt'); %modo texto - elimina o CR à partida
A=fread(fid);%,'ubit1');
Comp=length(A);
Simb=[];
Ocorr=[];
for i=1:Comp
%length(Ocorr)+1
if isempty(Simb)
Simb(1)=A(i,1);
Ocorr(1)=1;
else
j=length(Simb);
while j~=0
if A(i,1)==Simb(j)
break;
end
j=j-1;
end
if j==0
%length(Simb)+1;
Simb(length(Simb)+1)=A(i,1);
Ocorr(length(Ocorr)+1)=1;
else
Simb(j)=A(i,1);
Ocorr(j)=Ocorr(j)+1;
end
end
end
Prob=Ocorr/sum(Ocorr);
P=sum(Prob); %para efeitos de teste: tem de ser 1
Simb=Simb';
Simb=char(Simb);
Simb=cellstr(Simb);
Simb=Simb';
From: Roger Stafford on 3 May 2010 15:01
fckool <xtrangekid(a)sapo.pt> wrote in message <1976149983.64477.1272906270072.JavaMail.root(a)gallium.mathforum.org>...
> hi.. I have this code, and i want optimize it.. any suggestion?
> .......

I've done this in haste and haven't tried it out, but here is my idea. If it isn't right, something similar should work.

[u,m,n] = unique(A,'first');
c = histc(A,u);
[t,p] = sort(m);
Simb = u(p);
Ocorr = c(p);

This just calculates 'Simb' and 'Ocorr'. The rest looks straightforward.

Roger Stafford
From: fckool on 3 May 2010 11:36
wow... it seems work.

Can you do a small explanation ?


Thank you
From: Roger Stafford on 3 May 2010 16:14
fckool <xtrangekid(a)sapo.pt> wrote in message <845054490.65201.1272915427662.JavaMail.root(a)gallium.mathforum.org>...
> wow... it seems work.
> Can you do a small explanation ?
> Thank you

If I understand your code correctly, what it does is to list in 'Simb' the first appearances of unique elements in A in the order of those appearances. In 'Ocorr' is placed a count of the total number of appearances for each corresponding value in 'Simb'. However, as you apparently surmised, the algorithm is not very efficient.

The calls "[u,m,n] = unique(A,'first')" and "c = histc(A,u)" do this in a more efficient manner, with the unique elements of A being placed in u and corresponding counts in c. However they are in sorted order of u elements instead of order of occurrence in A. Fortunately, the values in m give the indices for the first occurrences in A of the elements in u if the 'first' option is used.

Therefore we must do a sort on m to find the necessary permutation, p, that needs to be performed on u and c elements to reorder them in the order of their original occurrences in A instead of their numerical order in u.

Roger Stafford
From: fckool on 12 May 2010 17:38
hello

Ok, i think i understood that.

I have other question:

who can i detect the ASCII code 10 (line-feed) and subtract it in 'Simb' and one value on 'Occur'?

Thank you
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