Thread Subject: changs arrays without using " if/end "

Assume that I have a matrix, say A, with 10^6 arrays. I want
to change any array which is less than zero to zero. Also, I
do not want to use 'if/end' and check each array.
Any idea?

"Hosein " <Kalaeimh@yahoo.com> wrote in message
<g4bige$qqe$1@fred.mathworks.com>...
> Assume that I have a matrix, say A, with 10^6 arrays. I want
> to change any array which is less than zero to zero. Also, I
> do not want to use 'if/end' and check each array.
> Any idea?

help max

John

In article <g4bige$qqe$1@fred.mathworks.com>,
Hosein <Kalaeimh@yahoo.com> wrote:
>Assume that I have a matrix, say A, with 10^6 arrays. I want
>to change any array which is less than zero to zero. Also, I
>do not want to use 'if/end' and check each array.
>Any idea?

I suspect that you mean that you have a matrix with 10^6 -entries-,
(or "array elements"), not with 10^6 sub-arrays. Otherwise it
would be necessary for you to define what it means for
an "array" to be less than 0.

If you are working with a numeric array, then

A(A < 0) = 0;

will do what you need.
--
  "There is nothing so bad but it can masquerade as moral."
                                              -- Walter Lippmann

"John D'Errico" <woodchips@rochester.rr.com> wrote in
message <g4bith$16s$1@fred.mathworks.com>...
> "Hosein " <Kalaeimh@yahoo.com> wrote in message
> <g4bige$qqe$1@fred.mathworks.com>...
> > Assume that I have a matrix, say A, with 10^6 arrays. I want
> > to change any array which is less than zero to zero. Also, I
> > do not want to use 'if/end' and check each array.
> > Any idea?
>
> help max
>
> John

John;
What do you mean?
Assume that I am not looking for less than zero. I am
looking for a number, say '5'. I want to find any array
which equals to '5' and change it to zero.

"Hosein " <Kalaeimh@yahoo.com> wrote in message
<g4bige$qqe$1@fred.mathworks.com>...
> Assume that I have a matrix, say A, with 10^6 arrays. I want
> to change any array which is less than zero to zero. Also, I
> do not want to use 'if/end' and check each array.
> Any idea?

If by "array" you mean "element" (given that by my
definition an array is a matrix) then you can use logical
indexing. Code:

A = rand(5,99);
A(A<0.5) = 0;

will set all values in matrix 'A' that are less than 0.5 to 0.

Chris

roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) wrote in
message <g4bj1l$jfg$1@canopus.cc.umanitoba.ca>...
> In article <g4bige$qqe$1@fred.mathworks.com>,
> Hosein <Kalaeimh@yahoo.com> wrote:
> >Assume that I have a matrix, say A, with 10^6 arrays. I want
> >to change any array which is less than zero to zero. Also, I
> >do not want to use 'if/end' and check each array.
> >Any idea?
>
> I suspect that you mean that you have a matrix with 10^6
-entries-,
> (or "array elements"), not with 10^6 sub-arrays. Otherwise it
> would be necessary for you to define what it means for
> an "array" to be less than 0.
>
> If you are working with a numeric array, then
>
> A(A < 0) = 0;
>
> will do what you need.
> --
> "There is nothing so bad but it can masquerade as moral."
> -- Walter
Lippmann

You are right. Probably I should say "array elements"

Anyway. Your answer is exactly what I was looking for.
Thanks

"Hosein " <Kalaeimh@yahoo.com> wrote in message
<g4bjan$52v$1@fred.mathworks.com>...
> "John D'Errico" <woodchips@rochester.rr.com> wrote in
> message <g4bith$16s$1@fred.mathworks.com>...
> > "Hosein " <Kalaeimh@yahoo.com> wrote in message
> > <g4bige$qqe$1@fred.mathworks.com>...
> > > Assume that I have a matrix, say A, with 10^6 arrays. I want
> > > to change any array which is less than zero to zero. Also, I
> > > do not want to use 'if/end' and check each array.
> > > Any idea?
> >
> > help max
> >
> > John
>
> John;
> What do you mean?
> Assume that I am not looking for less than zero. I am
> looking for a number, say '5'. I want to find any array
> which equals to '5' and change it to zero.

No, if you re-read your original statement,
you were looking for any element which was
less than zero, and changing that element
to zero. This does EXACTLY that.

  X = max(X,0);

If you change the problem, then I'd change
my answer. But does that really seem fair?

If you now want to reset any element which
was equal to 5, and turn those elements to
zero, then I'd have told you to do this:

  X(X==5) = 0;

Want to change it again? I hate chasing
moving targets, though. ;-)

John