How can I get randperm function to calculate assigned percentage and values?

I need to calculate that out of 1000000 elements, 75% should be randomly assigned a value of 1.5.

‘p = randperm(n)’ to specify which element is assigned with the properties of inclusions, where ‘n’ is the total number of elements (1000000), ‘p’ contains randomly ordered numbers from ‘1’ to ‘n’. Then, I need to assign the first ‘m’ elements with the value (1.5)

Out of 1000000 elements, 75% should be randomly assigned a value of 1.5.

‘n’=1000000

‘m’=1.5

Answer 1

[Keshav]

Based on my understanding, you want to generate an array of size n such that random 75% elements value is 1.5.

you can use the below code to do so.

n = 1000000;
p = randperm(n);
array = zeros(n,1);
num = .75*n;
for i = 1:num
    array(p(i)) = 1.5;
end
% if you want you can assign some other value to the remaining elements
%for i = num+1:n
%    array(p(i)) = some_other_val
%end

Answer 2

[Steven Lord]

Let's look at a slightly smaller problem.

A = zeros(10);
numElements = numel(A)

numElements = 100

numDesired = ceil(0.25*numElements)

numDesired = 25

elementsToSet = randperm(numElements, numDesired)

elementsToSet = 1×25

80 78 77 26 7 38 96 65 99 57 14 15 42 10 81 86 8 51 90 30 1 22 47 33 62

A(elementsToSet) = 1

A = 10×10

1 0 0 0 0 1 0 0 1 0 0 0 1 0 1 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 1 1 0 0 0 1 1 0 1 0 0 1 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 1 0 1 0 0 0 0 1 1 0

howManyNonzeroElements = nnz(A) % Should be numDesired

howManyNonzeroElements = 25

Alternately if you're working with sparse matrices you should look at sprand, sprandn, and sprandsym instead.