# could anyone help me how to generate two different random numbers of same value.

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jaah navi il 5 Lug 2021
Commentato: jaah navi il 6 Lug 2021
I am having two matrices A and B generated randomly with different values
A=rand(4,3)
B=rand(4,3)
Now I want to know is there any other way such that the some of the values generated in A can be made equal to the values generated in B.
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Yongjian Feng il 5 Lug 2021
Not very sure what you need here. Since rand is random, it is possible already some of the values in A can be repeated in B.
1. Do you want the sum of A is the same as the sum of B?
2. Do you want exactly 3 (for examples) values in A to be already repeated in B?
jaah navi il 5 Lug 2021
Yes, I know that some of the values in A can be repeated in B.
In my case, the size of A and B is very large i.e, (48000,1). When I generate i can find only minimum number of values remains to be same i.e, fo example 2300 out of 48000. But I want the maximum number of values to be same i.e, 45700/48000.
Could you please hlp me onthis.

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### Risposta accettata

Steven Lord il 5 Lug 2021
A = rand(5, 5);
A1 = A; A2 = A; % Make copies for later comparison
B = rand(5, 5);
numberOfMatches = 6;
locationOfMatchesInB = randperm(numel(B), numberOfMatches);
If you want the elements from B to be in exactly the same locations in A:
A1(locationOfMatchesInB) = B(locationOfMatchesInB);
If you want the elements from B to be put in some location, but not necessarily the same locations, in A:
locationOfMatchesInA = randperm(numel(A), numberOfMatches);
A2(locationOfMatchesInA) = B(locationOfMatchesInB);
Now compare:
A
A = 5×5
0.9605 0.1936 0.1763 0.7655 0.5840 0.6432 0.6447 0.2002 0.5192 0.1195 0.8839 0.0211 0.4184 0.5463 0.9373 0.2247 0.7324 0.8192 0.9718 0.4654 0.3539 0.5847 0.8463 0.1017 0.9999
A1
A1 = 5×5
0.3280 0.1936 0.1763 0.7655 0.7112 0.6432 0.6447 0.2002 0.5192 0.7247 0.8839 0.9045 0.3648 0.5463 0.9373 0.2247 0.7324 0.8192 0.9718 0.4654 0.4195 0.5847 0.8463 0.1017 0.9999
A2
A2 = 5×5
0.9605 0.1936 0.1763 0.7655 0.5840 0.7112 0.6447 0.2002 0.5192 0.1195 0.8839 0.7247 0.4184 0.5463 0.9373 0.2247 0.9045 0.3280 0.9718 0.4195 0.3648 0.5847 0.8463 0.1017 0.9999
B
B = 5×5
0.3280 0.3758 0.7772 0.0375 0.7112 0.4655 0.5999 0.1197 0.2314 0.7247 0.4005 0.9045 0.3648 0.0259 0.9559 0.6848 0.5505 0.0491 0.4264 0.4717 0.4195 0.3723 0.9590 0.2997 0.9910
Where did A1 flip?
[sort(locationOfMatchesInB).', find(A1 ~= A)]
ans = 6×2
1 1 5 5 8 8 13 13 21 21 22 22
What changed?
A1(A1 ~= A)
ans = 6×1
0.3280 0.4195 0.9045 0.3648 0.7112 0.7247
B(A1 ~= A)
ans = 6×1
0.3280 0.4195 0.9045 0.3648 0.7112 0.7247
##### 2 CommentiMostra NessunoNascondi Nessuno
jaah navi il 6 Lug 2021
For the code,
A = rand(5, 5);
A1 = A; A2 = A; % Make copies for later comparison
B = rand(5, 5);
numberOfMatches = 6;
locationOfMatchesInB = randperm(numel(B), numberOfMatches);
Is there any way to make it invisible in the code
numberOfMatches
Walter Roberson il 6 Lug 2021
A = rand(5, 5);
A1 = A; A2 = A; % Make copies for later comparison
B = rand(5, 5);
locationOfMatchesInB = randperm(numel(B), 6);

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### Più risposte (2)

Amit Bhowmick il 5 Lug 2021
Modificato: Amit Bhowmick il 5 Lug 2021
Check the values you will alyas get zero that is they are not equal. More preciesly probability of getting same value is very less. Basically the algorithm of generating random number is such you can learn here
https://en.wikipedia.org/wiki/Random_number_generation
rand(4,3)==rand(4,3) or isequal(rand(4,3),rand(4,3))
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Walter Roberson il 5 Lug 2021
A = sort(rand(300,300));
imagesc(A)
title('original')
p = 45700/48000;
B = reshape(B(randperm(numel(B))), size(A));
imagesc(B)
title('rerandom')
mean(ismember(B(:), A)) * 100
ans = 95.2233
p * 100
ans = 95.2083
So in this case, the target fraction to keep was 95.2083% and the actual fraction kept was 95.2233%
If it was necessary to have exactly the ratio 45700/48000 stay the same then that could be done... though it becomes trickier if you are working with integers.
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Walter Roberson il 6 Lug 2021
A = arrayfun( @my_rand, repelem((1:10).',30), 'UniformOutput', false);
B = arrayfun( @my_rand, repelem((1:10).',30), 'UniformOutput', false);
p = 0.9;
nkeep = ceil(p * numel(A)) ;
keepidx = randperm(numel(A), nkeep);
B(keepidx) = A(keepidx);
jaah navi il 6 Lug 2021

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