Delete some specific numbers from an array

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Rongyu Chu 2019-10-2

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https://ww2.mathworks.cn/matlabcentral/answers/483144-delete-some-specific-numbers-from-an-array

编辑： Andrei Bobrov 2019-10-3

So, the problem is like this. I have an array of random numbers. For example [10 9 5 5 7 3 5 8 3 5 6 3 7 10 ]. First, I have to delete some of the numbers to make any point's value can not between its adjecent numbers. For example 9 is between 10 and 5, so I will delete 9. I tried to use a for loop but that does not work.

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Walter Roberson 2019-10-2

Hint: sign(diff(TheVector)) will be the same for two entries in a row if the middle value is between the two other values (or if the three values are all equal)

Andrei Bobrov 2019-10-3

We delete 7, 7 is between 3 ans 10?

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Answer 1

Andrei Bobrov 2019-10-2

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https://ww2.mathworks.cn/matlabcentral/answers/483144-delete-some-specific-numbers-from-an-array#answer_394392

编辑：Andrei Bobrov 2019-10-3

在 MATLAB Online 中打开

A = [10 9 5 5 7 3 5 8 3 5 6 3 7 10 ];
B = sign(diff(A(hankel(1:3,3:numel(A)))',1,2));
out = A(   [true;  prod(B,2) ~= 1 ; true]     );

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Rongyu Chu 2019-10-3

My final purpose is not just delete 9 among 10 and 5. This is just an example. I will have a dat file which contians over 10,000 numbers and I need it to process automatically. Thank you for your help.

Andrei Bobrov 2019-10-3

I'm fix.

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Answer 2

Rongyu Chu 2019-10-3

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https://ww2.mathworks.cn/matlabcentral/answers/483144-delete-some-specific-numbers-from-an-array#answer_394562

So, here is the cide I wrote.

N = load('exp.dat');

len = length(N);

for i = 2:(len-3)

if N(i+1)>N(i)>N(i-1)

N(i) = [];

len = len - 1;

%i = i - 1;

elseif N(i+1)<N(i)<N(i-1)

N(i) = [];

len = len - 1;

%i = i - 1;

end

I tired to use if sentence to compare the value and delete those numers whose value is in the middle of its adjcent numbers. However, this code does not work well. I am wondering why.

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Rongyu Chu 2019-10-3

thank you. I realized that problem. But now I found a new problem. After I delete some numbers from an array, the arrat size gonna change. So it's not always len-1. But, how should I update that information ?