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# Finding a range in an array

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Rafay Ali on 27 May 2019
Edited: madhan ravi on 27 May 2019
I have an array of 8000 values. I want to find a range of particular values say for example the values which are between 20 - 25.6 should be multiplied by -1 but the values should be in changed in the same array. I am currently using a the find nested in an if but somehow I cannot store it in the same array.
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Rafay Ali on 27 May 2019
In one of my searches, I came across this. Will it be possible for me to make it
r(r>2) = r * -1;
% Generate random data between -3 and 3
a = -3;
b = 3;
r = (b-a).*rand(100,1) + a;
r(r>2) = 2 ; % Change numbers greater then 2
r(r<0) = 0 ;% Change numbers less then 0

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### Accepted Answer

madhan ravi on 27 May 2019
Edited: madhan ravi on 27 May 2019
idx = (array>=20) & (array<=25.6);
array(idx) = -array(idx)
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madhan ravi on 27 May 2019
I suggest you to do MATLAB onramp course to cover the basics of MATLAB.
idx = (array>=20) & (array<=25.6); % using this as indices is already much more efficient than find()
indices = find(idx) % this would give you the indices where the condition satisfies
array(2222 : 2245) = - some_number * array(2222 : 2245)

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### More Answers (1)

Andrei Bobrov on 27 May 2019
Let A - your array.
Anew = A.*(1 - 2*(A >= 20 & A <= 26.5));
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