alternate to using "find" to determine indices?

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David W Purcell 2020-4-1

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评论： David W Purcell 2020-4-1

Hello,

I have three logical vectors that reflect some characteristics of a modelled set of items.

At one point, I determine a small set of items that have a certain characteristic, but not two others, using find to determine their indices:

smallList=find(iList & ~rList & ~dList); %iList, rList, and dList are logical vectors

Is there a way to determine their indices using logical indexing or something else faster than find? I've had trouble wrapping my head around how I might achieve that.

Thank you for considering, David

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Answer 1

Adam Danz 2020-4-1

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编辑：Adam Danz 2020-4-1

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"Is there a way to determine their indices using logical indexing...?"

Yes, and logical indexing is usually a better way to index than using a linear index or subscripts, and you've already discovered how to do it :)

logicalIndex = iList & ~rList & ~dList;

" I've had trouble wrapping my head around how I might achieve that."

Here's a general demo

data = rand(5,10);  % random values between 0 and 1
idx = data <0.5;    % logical index of values less than 0.5
data(idx) = NaN;    % Replaces values < 0.5 with NaNs

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Adam Danz 2020-4-1

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In that case, find() is what you should use if you're working with a loop.

linIdx = find(logicalIndex); 
for i = 1:numel(linIdx)
    myFunction(h(linIdx(i)));  % h is your vector of class obj.
end

Depending on the complexity of the function you're applying to each object, you could use arrayfun() or cellfun() to apply the function to each element of the array.

David W Purcell 2020-4-1