Thread Subject: for loop and comparisons

hi all,

I am new to Matlab, so please bare with me.
I have 2 cell arrays and I want to compare each element in
one to each element in the other. However, when I create a
for loop like this
(as an example)
i=1:100
if A{i}==2*B{i}, B{i}=[], end
end
It only compares the 1st element to the 1st, the 2nd to the
2nd and so on.
Is there a way to change this, or another approach that I
should take?
thank you in advance, any help is appreciated!

"KA " <kmcdon03@uoguelph.ca> wrote in message
<g38gt9$h35$1@fred.mathworks.com>...
> hi all,
>
> I am new to Matlab, so please bare with me.
> I have 2 cell arrays and I want to compare each element in
> one to each element in the other. However, when I create a
> for loop like this
> (as an example)
> i=1:100
> if A{i}==2*B{i}, B{i}=[], end
> end
> It only compares the 1st element to the 1st, the 2nd to the
> 2nd and so on.
> Is there a way to change this, or another approach that I
> should take?
> thank you in advance, any help is appreciated!
>
Hi
you have to do a double loop (maybe there is a convenient
way to vectorize but if you're new it's better to do it this
way first)

for i=1:length(A)
   for j=1:lenth(B)
      if A{i}==2*B{j}
          B{j}=[];%See Note
      end
end

Note : if you do this you won't compare B{j} anymore...

Note2 : to do == comparison be sure that each A{i} and B{i}
are scalars (so why using cell array here instead of matrix ?)

Caroline

"KA " <kmcdon03@uoguelph.ca> wrote in message
<g38gt9$h35$1@fred.mathworks.com>...
> hi all,
>
> I am new to Matlab, so please bare with me.
> I have 2 cell arrays and I want to compare each element in
> one to each element in the other. However, when I create a
> for loop like this
> (as an example)
> i=1:100
> if A{i}==2*B{i}, B{i}=[], end
> end
> It only compares the 1st element to the 1st, the 2nd to the
> 2nd and so on.
> Is there a way to change this, or another approach that I
> should take?
> thank you in advance, any help is appreciated!
>
>

Given the statement 2 * B{i} I assume that each cell of A
and B holds a double array?
Are all these arrays the same size?
Can you convert them into one big matrix using CAT?

If so, use RESHAPE to make them a 2D array with each row
holding one cell of the original arrays, and use ISMEMBER or
SETDIFF with the rows option, to look for similaraties
and/or differences between A and B.


In pseudocode:

A2 = cat(..,A{:}) ;
A3 = reshape(A2,...)

C = setdiff(A3,B3,'rows')

hth
Jos

"Jos " <DELjos@jasenDEL.nl> wrote in message
<g38hg0$nlb$1@fred.mathworks.com>...
> "KA " <kmcdon03@uoguelph.ca> wrote in message
> <g38gt9$h35$1@fred.mathworks.com>...
> > hi all,
> >
> > I am new to Matlab, so please bare with me.
> > I have 2 cell arrays and I want to compare each element in
> > one to each element in the other. However, when I create a
> > for loop like this
> > (as an example)
> > i=1:100
> > if A{i}==2*B{i}, B{i}=[], end
> > end
> > It only compares the 1st element to the 1st, the 2nd to the
> > 2nd and so on.
> > Is there a way to change this, or another approach that I
> > should take?
> > thank you in advance, any help is appreciated!
> >
> >
>
> Given the statement 2 * B{i} I assume that each cell of A
> and B holds a double array?
> Are all these arrays the same size?
> Can you convert them into one big matrix using CAT?
>
> If so, use RESHAPE to make them a 2D array with each row
> holding one cell of the original arrays, and use ISMEMBER or
> SETDIFF with the rows option, to look for similaraties
> and/or differences between A and B.
>
>
> In pseudocode:
>
> A2 = cat(..,A{:}) ;
> A3 = reshape(A2,...)
>
> C = setdiff(A3,B3,'rows')
>
> hth
> Jos

Sorry I made a mistake in the example, that should not have
been 2*B{i}. I am actually working with 3x3 matrices. The 2
should have just been another variable because each matrix
is multiplied by another matrix. I am not using scalars.
thank you for your help!