Finding a range in an array

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.

[Rafay Ali]

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

Answer 1

[madhan ravi]

 idx = (array>=20) & (array<=25.6);
 array(idx) = -array(idx)

[Rafay Ali]

Thanks and is it possible that instead of these particular values I go particular index values? For example, make all the values between 2222 to 2245 be multiplied by a negative number.

[madhan ravi]

https://in.mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html

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)

Answer 2

[Andrei Bobrov]

Let A - your array.

Anew = A.*(1 - 2*(A >= 20 & A <= 26.5));