Logical Vectors From Values - comp.soft-sys.matlab

Walter Roberson wrote: > james bejon wrote: >> Dear All, Is there a neat way of getting from, say, >> >> [3, 5, 8] >> >> to >> >> [0, 0, 1, 0, 1, 0, 0, 1]? > > B = false(1,max(A)); > B(A) = true; Additional note: if there can be big gaps between the true values, then you may wish to consider using sparse arrays. Sparse arrays are supported for values of class double, and values of class logical, but (not as yet) for any other class.

james bejon wrote: > Dear All, Is there a neat way of getting from, say, > > [3, 5, 8] > > to > > [0, 0, 1, 0, 1, 0, 0, 1]? Alternately, o(x)=1; % create the 0/1 vector l = logical(o); % turn it into a logical one Too bad for things like this ML doesn't support nested assignment.. l = logical(o(x)=1); % Doesn't work, of course... :( --

On Mar 30, 2:37=A0pm, dpb <n...@non.net> wrote: > james bejon wrote: > > Dear All, =A0Is there a neat way of getting from, say, > > > [3, 5, 8] > > > to > > > [0, 0, 1, 0, 1, 0, 0, 1]? > > Alternately, > > o(x)=3D1; =A0 =A0 =A0 =A0 =A0% create the 0/1 vector > l =3D logical(o); =A0% turn it into a logical one > > Too bad for things like this ML doesn't support nested assignment.. > > l =3D logical(o(x)=3D1); =A0 % Doesn't work, of course... :( > > -- If you were going to do that, why not just make it logical in the first place? o(x) =3D true; -Nathan

Nathan wrote: .... > If you were going to do that, why not just make it logical in the > first place? > > o(x) = true; Primarily because... >> which true true not found. >> help true true.m not found. >> :( --

dpb wrote: > james bejon wrote: >> Dear All, Is there a neat way of getting from, say, >> >> [3, 5, 8] >> >> to >> >> [0, 0, 1, 0, 1, 0, 0, 1]? > > Alternately, > > o(x)=1; % create the 0/1 vector > l = logical(o); % turn it into a logical one > > Too bad for things like this ML doesn't support nested assignment.. > > l = logical(o(x)=1); % Doesn't work, of course... :( Well, if you are going to be like that! l = any(bsxfun(@eq,1:max(x),x.'));

dpb <none@non.net> wrote in message <hotrs9$qbg$1@news.eternal-september.org>... > Nathan wrote: > ... > > > If you were going to do that, why not just make it logical in the > > first place? > > > > o(x) = true; > > Primarily because... > > >> which true > true not found. > >> help true > > true.m not found. > > >> > > :( > > -- Of course, you could fix that! function T = true(N) % Hacky-TRUE T = ~zeros(N);

"james bejon" <jamesbejon@yahoo.co.uk> wrote in message <hotso5$2ib$1@fred.mathworks.com>... > Thanks for all the really helpful replies! > > I'm currently toying with the (perhaps hungry?) expression: > > ismember((1:A(end)), A) > > (I can assume A is in ascending order) That works, but it will be slower and less readable than many of the other solutions.

dpb wrote: > Nathan wrote: > ... > >> If you were going to do that, why not just make it logical in the >> first place? >> >> o(x) = true; > > Primarily because... > > >> which true > true not found. > >> help true > > true.m not found. But if you have logical() at your disposal, then you could use o(x) = logical(1); So now who is going to give us an answer in terms of logical(accumarray(...)) ? ;-)

Walter Roberson > dpb wrote: > > Nathan wrote: > > ... > > > >> If you were going to do that, why not just make it logical in the > >> first place? > >> > >> o(x) = true; > > > > Primarily because... > > > > >> which true > > true not found. > > >> help true > > > > true.m not found. > > But if you have logical() at your disposal, then you could use > > o(x) = logical(1); > > > So now who is going to give us an answer in terms of logical(accumarray(...)) > ? ;-) Out = accumarray(A.',true,[],@logical); Another versione :). Only if unique(A) == A.

Oleg Komarov wrote: .... >> But if you have logical() at your disposal, then you could use >> >> o(x) = logical(1); >> .... Indeedy, do...very good (and why didn't _I_ think of it??? :( )... :) --

Matt Fig wrote: > dpb <none@non.net> wrote in message > <hotrs9$qbg$1@news.eternal-september.org>... >> Nathan wrote: >> ... >> >> > If you were going to do that, why not just make it logical in the >> > first place? >> > > o(x) = true; >> >> Primarily because... >> >> >> which true >> true not found. >> >> help true >> >> true.m not found. >> >> >> >> >> :( >> >> -- > > > Of course, you could fix that! > > function T = true(N) > % Hacky-TRUE > T = ~zeros(N); true(aye-that); --

Walter Roberson wrote: > dpb wrote: >> james bejon wrote: >>> Dear All, Is there a neat way of getting from, say, >>> >>> [3, 5, 8] >>> >>> to >>> >>> [0, 0, 1, 0, 1, 0, 0, 1]? >> >> Alternately, >> >> o(x)=1; % create the 0/1 vector >> l = logical(o); % turn it into a logical one >> >> Too bad for things like this ML doesn't support nested assignment.. >> >> l = logical(o(x)=1); % Doesn't work, of course... :( > > Well, if you are going to be like that! > > l = any(bsxfun(@eq,1:max(x),x.')); Chuckle... --

Oleg Komarov wrote: >> So now who is going to give us an answer in terms of >> logical(accumarray(...)) ? ;-) > > Out = accumarray(A.',true,[],@logical); > > Another versione :). Only if unique(A) == A. Out = logical(accumarray(A.', 1)); This version does not require unique(A) == A. I am not at all experienced in accumarray, but looking at the documentation, it appears to me that your version would also work with repeated elements if you changed the @logical to @any .

There's some really neat stuff here. Thanks so much. I'm very new to Matlab, but am starting to see how concise its code can be. On a related note, Can anyone think of a neat way of converting, say, [3, 8, 12] to [1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3]? Or better still: [3, 8, 12; 3, 7, 12] to [1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3; 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3]?

Walter Roberson <roberson@hushmail.com> wrote in message <houedm$r10$1@canopus.cc.umanitoba.ca>... > Oleg Komarov wrote: > > >> So now who is going to give us an answer in terms of > >> logical(accumarray(...)) ? ;-) > > > > Out = accumarray(A.',true,[],@logical); > > > > Another versione :). Only if unique(A) == A. > > Out = logical(accumarray(A.', 1)); > > This version does not require unique(A) == A. > > I am not at all experienced in accumarray, but looking at the > documentation, it appears to me that your version would also work with > repeated elements if you changed the @logical to @any . You're right! Oleg

"james bejon" > There's some really neat stuff here. Thanks so much. I'm very new to Matlab, but am starting to see how concise its code can be. On a related note, Can anyone think of a neat way of converting, say, > > [3, 8, 12] > > to > > [1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3]? > > Or better still: > > [3, 8, 12; > 3, 7, 12] > > to > > [1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3; > 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3]? Be rude! A = [3,8,12]; rude(A./(1:numel(A)), 1:numel(A)) % FEX by us Oleg

"james bejon" <jamesbejon@yahoo.co.uk> wrote in message <housrl$1vl$1@fred.mathworks.com>... > There's some really neat stuff here. Thanks so much. I'm very new to Matlab, but am starting to see how concise its code can be. On a related note, Can anyone think of a neat way of converting, say, > > [3, 8, 12] > > to > > [1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3]? > > Or better still: > > [3, 8, 12; > 3, 7, 12] > > to > > [1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3; > 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3]? c=[3, 8, 12; 3, 7, 12] r = repmat((1:size(c,1)).',[1 size(c,2)]); A = accumarray([r(:) c(:)+1],1); A(:,1) = 1; A = cumsum(A,2); A(:,end) = []; disp(A) % Bruno

Hi Bruno. Thanks very much for your suggestion. Works perfectly. I like your idea with the cumsum function. In the end, I've gone for something like (I happen to know that all the rows are of length 25) c = transpose([3, 11, 23, 24; 3, 10, 23, 24]) + 1; z = zeros(25, size(c, 2)); n = repmat(1:size(c, 2), size(c, 1), 1); z(sub2ind(size(z), c, n)) = 1; z = cumsum(z, 1) + 1; P.S. I nicked the sub2ind idea from your following RANK thread! http://www.mathworks.com/matlabcentral/newsreader/view_thread/163003#731927

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