# how to replace the element with random number based if statement

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Genz on 16 Oct 2019
Commented: sid Chen on 17 Oct 2019
Helllo everyone
i have a problem to change element of array with iteration approach. refer to https://www.mathworks.com/matlabcentral/answers/8817-how-to-replace-the-elements-of-a-matrix-using-the-conditions-if-else , i have same problem but little different. for instance i have mut1 = [.11 .12 .13 .14 .15 .16 .17 .18 .19 .20] and constan number 0.5. i want to replace element of mut1 with 'random number between' if random number(rmi) < 0.5. so this is what iam doing.
mutC = zeros(size(mut1));
pm = 0.5;
for i = 1:numel(mut1)
rmi = rand(1,1)
rCm = rbC+(raC-rbC).*rand(1,1)
if rmi<pm
mutC = rCm
else
mutC = mut1
end
end
but the final result is always mutC = mut1. there is no number from rCm.
I will appreciate any help. thank you.

Andrei Bobrov on 16 Oct 2019
Edited: Andrei Bobrov on 16 Oct 2019
mutC = mut1;
[m,n] = size(mut1);
pm = 0.5;
rmi = rand(m,n);
rCm = rbC+(raC-rbC).*rand(m,n);
for i = 1:numel(mut1)
if rmi(i) < pm
mutC(i) = rCm(i);
end
end
or
pm = .5;
mutC = mut1;
[m,n] = size(mut1);
rCm = rbC+(raC-rbC).*rand(m,n);
lo = rand(m,n) < pm;
mutC(lo) = rCm(lo);

Genz on 16 Oct 2019
thank you for you fast reply sir. one more question sir. how i can store the random value "rCm'? because i have to submit 'rCm' value.
thank you.
Andrei Bobrov on 16 Oct 2019
I'm fix.
Genz on 16 Oct 2019
many thanks sir. 2 thumbs up..
GBU.

sid Chen on 16 Oct 2019
The problem is
if rmi<pm
mutC = rCm
else
mutC = mut1
with these code, you replace the whole matrix, all the elements are replaced.
To avoid this, you need to replace only one elements step by step. Just add an subscipt 'i' to point the element to be repalced.
if rmi<pm
mutC(i) = rCm(i)
else
mutC(i) = mut1(i)

Genz on 16 Oct 2019
when i run this code become error "index exceeds matrix dimensions"
sid Chen on 17 Oct 2019
if rmi<pm
mutC(i) = rCm % change here, rCm is a number,not a matrix
else
mutC(i) = mut1(i)

R2016b

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