Generate 10 numbers from matrix

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Ashante Isabella Bon 2021-9-23

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https://ww2.mathworks.cn/matlabcentral/answers/1459564-generate-10-numbers-from-matrix

评论： Ashante Isabella Bon 2021-9-27

采纳的回答： Image Analyst

Say I have a matrix, v1, how would I be able to randomly generate 10 numbers within the existing matrix?

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the cyclist 2021-9-23

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Do you mean that you have, for example, a 5x5 matrix such as

M = magic(5)
M = 5×5
  24     1     8    15
   5     7    14    16
   6    13    20    22
  12    19    21     3
  18    25     2     9

and you want to select 10 numbers from that matrix at random?

Can you select the same number twice, or all 10 should be from a different position?

How do you want the output? A vector of 10 numbers?

For you future reference, please understand that if you had spent more writing out a more complete, thoughtful question, we would not need to clarify what you need.

Ashante Isabella Bon 2021-9-27

Yes to first question, all different positions, Just 10 numbers no need to be a vector

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Answer 1

Image Analyst 2021-9-23

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To generate the numbers from random locations, without repeating any of the locations you need to use randperm(), not randi() like other answer(s). Using randi() will potentially allow the same location to be used multiple times. So use randperm() or randi() depending on what you want.

% Generate sample matrix -- a 7 row-by-9 column matrix.
m = randi(100, 7, 9)
% Get 10 random linear indexes with no location being a repeat:
randomIndexes = randperm(numel(m), 10)
% Extract data at those random locations:
extractedNumbers = m(randomIndexes)

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Answer 2

Sulaymon Eshkabilov 2021-9-23

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Based on what you've stated the following could be what you want to obtain:

v1 = randi(10, 5, 5)    %#ok   % Is existing matrix
v1 = 5×5
     2     5     2     1    10
     7     5     3     1     6
    10     4     4     1     9
     2     6     5     3     1
     8     5     2    10     2
IDX = randi([1, 10], 1, 10);   % Randomly select indexes from the existing matrix  
R = v1(IDX)                    % Randomly selected 10 numbers from v1
R = 1×10
     4     5     5    10     8     5     8     5     2     8