if statement for range of array values

Question

Trader 2012-5-9

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Is there a better way to write this 'if' statement?

for i = 1:size(somevalue)
if (x(i) < xmax && x(i-1) < xmax && x(i-2) < xmax) || (y(i) < ymax && y(i-1) < ymax)
disp('do something');
end

Thanks for your help!

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Oleg Komarov 2012-5-9

Trivial question, do you want the condition to be verified on any (&&) of the 3 consecutive values or on all (&)?

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Answer 1

Wayne King 2012-5-9

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How about

   if (any(x<xmax) || any(y<ymax))
    disp('do something');
   end

or do you really want to test if every one is? Of course it seems that x<xmax or y<ymax are to be always true.

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Jan 2012-5-9

@Sean: This needs to create a temporary array of the length numel(x)+numel(y). Therefore I assume this is slower than Wayne's approach.

Richard Brown 2012-5-9

Hence golf :)

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Answer 2

Dr. Seis 2012-5-9

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I think what you might be after is something like:

if all(x(i-1:i+1) < xmax) || all(y(i-1:i+1) < ymax)
   % something
end

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Dr. Seis 2012-5-9

Misinterpreted your "if" statement on my previous attempt. This should be what you are after.

Note: "all" will return TRUE if and only if the entire array returned from "x<xmax" is all 1's. "any" will return TRUE if there is one or more 1 in the array returned by "x<xmax".

Richard Brown 2012-5-9

If doing it this way, the x indices should be i-2:i, and the y indices should be i-1:i, and the loop should start at 3

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Answer 3

Richard Brown 2012-5-9

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To check I've understood correctly, you only want to do something if the current and two preceding x values are all less than xmax, or, the current and preceding y values are both less than ymax. Then, the indices you are interested in are given by:

idx = find(filter([1 1 1], 1, x < xmax) == 3 | filter([1 1], 1, y < ymax) == 2)

Note that 1 and 2 will never appear in idx as your expression cannot be evaluated for these