Select everything NOT returned by index
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Hello,
Apologies if this is a stupid question, but I haven't found a way to properly google it.
I have an index where certain conditions are met, but I want to make everything outside of that index NaN.
e.g.
x=find(wind(:,:,1)>0&wind(:,:,2)>0);
wind(x)=NaN; % But I actually want the parts not indexed to equal NaN
I'm looking for something like
wind(~x)=NaN
but that doesn't work. I can't just change my > sign around either because of the range of values in my matrix.
I'd just like to find a way to apply wind(x)=NaN to the values NOT in x.
Thanks, Claire
3 Comments
John D'Errico
on 26 Nov 2014
Edited: John D'Errico
on 26 Nov 2014
Claire - read my comment. See that Oleg did as I did, changed the & to an or. It is time to go back to basic logical operator school. Um, maybe Venn diagrams?
Accepted Answer
Roger Stafford
on 26 Nov 2014
You can always do logical indexing using the negation of whatever condition you have.
t = wind(:,:,1)>0&wind(:,:,2)>0;
wind(~t) = NaN;
2 Comments
More Answers (2)
John D'Errico
on 26 Nov 2014
Why can't you change the inequalities?
x=find(wind(:,:,1)<=0 | wind(:,:,2) <= 0);
I'm listening, but your statement makes no sense as to why not. Basic logic tells us that:
~(A & B) == ~A | ~B
As trivially,
x=find(~(wind(:,:,1)>0 & wind(:,:,2)>0));
Finally, and equally trivially, but considerably less efficient because it is an extra and wholly unnecessary step, you might read up on what setdiff does.
doc setdiff
4 Comments
Oleg Komarov
on 26 Nov 2014
Claire, you kept answering my comments and John's answer with your copy-paste text without even reading carefully. If there are two people telling you the same thing, and taking their time to do that in an elaborate clear way (John), it is not nice of you to paste the same sentences. I do not see much of an insult in the statement that you are missing the basics of logical truth tables (<http://en.wikipedia.org/wiki/Truth_table>) but an opportunity to go and check them out again, since much of programming is based on that.
Mallory Nation
on 25 Sep 2019
Edited: Mallory Nation
on 25 Sep 2019
For fun, to do what was wanted using find, you could do this:
xNot = setdiff(x,1:length(wind(:,:,1)));
wind(:,:,xNot) = nan;
But as already stated, the best way is to not use find at all.
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