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

Question

종현 김 2022-6-30

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https://ww2.mathworks.cn/matlabcentral/answers/1750865-how-can-i-get-randperm-function-to-calculate-assigned-percentage-and-values

回答： Steven Lord 2022-6-30

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

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Answer 1

Keshav 2022-6-30

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https://ww2.mathworks.cn/matlabcentral/answers/1750865-how-can-i-get-randperm-function-to-calculate-assigned-percentage-and-values#answer_996940

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

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Answer 2

Steven Lord 2022-6-30

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https://ww2.mathworks.cn/matlabcentral/answers/1750865-how-can-i-get-randperm-function-to-calculate-assigned-percentage-and-values#answer_996975

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