simple thresholding
in [Matlab]
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From: Mike on 4 May 2010 20:15 On May 4, 3:01 pm, Walter Roberson <rober...(a)hushmail.com> wrote: > Walter Roberson wrote: > > Mike wrote: > > >>>> d(:,:,1)(d(:,:,1)>8)=999 > >> ??? Error: ()-indexing must appear last in an index expression. > > >>>> dd=d(:,:,1);dd(dd>8)=999 > > >> dd = > > >> 8 1 6 > >> 3 5 7 > >> 4 999 2 > > >> Is there a way not to create a temporary "dd"? > > > Yup. > > > d(vertcat(d(:,:,1)>8, false(size(d,1)*size(d,2),1))) = 999; > > > Didn't say it would be short or easy to understand. > > Or error-proof either. I should have written, > > d(vertcat(d(:,:,1)>8, false(prod(size(d)-[0 0 1]),1))) = 999; > > Though now that I think of it, > > d(find(d(:,:,1)>8)) = 999; > > should work as well. > > Both versions will break if fixed index being searched over does not > happen to be 1, but I suspect more people would get a hint on changing > the code from the longer version; the reason the second shorter one > works for the first dimension only is more obscure... which is probably > why I used the more general version of it in a posting a few years ago ;-)- Hide quoted text - > Another one: >> a=magic(3);b=a+1;c=a+2; >> d=cat(3,a,b,c) d(:,:,1) = 8 1 6 3 5 7 4 9 2 d(:,:,2) = 9 2 7 4 6 8 5 10 3 d(:,:,3) = 10 3 8 5 7 9 6 11 4 >> find(d(:,:,3)>10) % set these elements to be 999. ans = 6 >> d(find(d(:,:,3)>10))=999. % pitfall d(:,:,1) = 8 1 6 3 5 7 4 999 2 d(:,:,2) = 9 2 7 4 6 8 5 10 3 d(:,:,3) = 10 3 8 5 7 9 6 11 4 I know why this is wrong. I am just thinking how it can be naturally written. Mike
From: Walter Roberson on 4 May 2010 22:09 Mike wrote: > Another one: >>> a=magic(3);b=a+1;c=a+2; >>> d=cat(3,a,b,c) >>> find(d(:,:,3)>10) % set these elements to be 999. > > ans = > > 6 > >>> d(find(d(:,:,3)>10))=999. % pitfall > I know why this is wrong. I am just thinking how it can be naturally > written. >> d(cat(3,false(size(d)-[0 0 1]),d(:,:,3)>10)) = 999 d(:,:,1) = 8 1 6 3 5 7 4 9 2 d(:,:,2) = 9 2 7 4 6 8 5 10 3 d(:,:,3) = 10 3 8 5 7 9 6 999 4
From: Walter Roberson on 4 May 2010 22:14
Walter Roberson wrote: > Mike wrote: > >> Another one: >>>> a=magic(3);b=a+1;c=a+2; >>>> d=cat(3,a,b,c) > >>>> find(d(:,:,3)>10) % set these elements to be 999. >> >> ans = >> >> 6 >> >>>> d(find(d(:,:,3)>10))=999. % pitfall > >> I know why this is wrong. I am just thinking how it can be naturally >> written. > >> d(cat(3,false(size(d)-[0 0 1]),d(:,:,3)>10)) = 999 d(2*size(d,1)*size(d,2)+find(d(:,:,3)>10)) = 999 |