Creating arrays of unknown length
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I am trying to write a function that generates a sequence of random integer numbers between 1 and m, stopping when a value is repeated for the first time. The function would generate an array containing all the numbers generated except for the last value that is a repeated occurrence. For example, if the generated sequence is 3 1 9 5 7 2 5, the array to be returned should be 3 1 9 5 7 2. Below is the code that I have so far; I feel that I am close, but that I'm missing smth trivial. Any insight would be extremely appreciated.
function [v] = sequence_CM(m)
for i=1:m
A(i)=ceil(2+((100+100)*rand(1)));
B(i)=A(i);
for k=((i+1):length(B))
if B(i)==A(i+1)
break;
end
end
end
v=A;
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Walter Roberson
2015년 12월 30일
Your code is treating m as a maximum length, with the generated values being integers in the range 3 to 202. But your description implies that m should be the maximum allowed random value -- which would also provide a natural maximum length by the pigeon hole principle (you cannot generate more than m different random integers in the range 1 to m without there being a duplicate.)
Your code is adding the new test value to both A and B, and is returning the full A. But when a duplicate is finally generated it is not to be put into the answer, according to your description.
It seems a waste of effort to maintain your B vector.
Hint: ismember(newvalue, A) and if it is not there then append newvalue to A, otherwise stop.
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Walter Roberson
2015년 12월 31일
A(i) is always already a member of A. Notice I referred to "newvalue" -- that is, generate a value without immediately storing it, and test to see if it is already there.
추가 답변 (2개)
Image Analyst
2015년 12월 31일
You can use unique and check the length of it. If there are repeats, the length of hte unique array will be less than the original array. Not sure how fast it is, but it works.
m = 10 % whatever you want.
randomIntegers = randi(m, 1, m)
for k = 2 : length(randomIntegers)
% Get the array from index 1 up to index k.
thisArray = randomIntegers(1:k)
% Check if the number of unique numbers matches the length of the array.
% If it does, all are unique and there are no repeats.
% If it does not, then there must now be a repeat.
if length(unique(thisArray)) < k
% There must be a duplicate.
break
end
end
% Extract numbers just up to index (k-1) - we don't want the repeated integer.
randomIntegers = randomIntegers(1:k-1)
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