How to randomly swap 2 elements in an array?
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Suppose that I have the below array:
C= [1 6 5 10 1 2 11 8 2 7 3 7 9 9]
How can I swap randomly only the elements inside the bold numbers
Assume after swap 11 and 3 : C= [1 6 5 10 1 2 3 8 2 7 11 7 9 9]
or swap 10 and " " between 9 9: C= [1 6 5 1 2 11 8 2 7 3 7 9 10 9]
采纳的回答
I'm going to assume at least one of the swap elements must be an number, and that the swapped numbers are allowed to have the same value (so you can some one 9 with another 9).
C= [1 6 5 10 1 2 11 8 2 7 3 7 9 9];
bold=[1 5 6 9 10 12 13 14];
C_temp=cell(1,2*numel(C));
C_temp(2:2:end)=num2cell(C);
valid_idx=1:numel(C_temp);
valid_idx(bold*2)=[];
swap_idx=[1 1];%invalid output to enter the loop
while ~any(mod(swap_idx,2)==0) || ... %at least 1 needs to be a number
swap_idx(1)==swap_idx(2) %the indices must be different
swap_idx=valid_idx(randperm(numel(valid_idx),2));
end
%perform swap
C_temp(swap_idx)=C_temp(swap_idx(end:-1:1));
D=cell2mat(C_temp);
clc,disp(C),disp(D)
12 个评论
Rik
2019-5-1
You didn't describe how you get the bold numbers, so you'll have to figure that out from your input. I might be able to help you there, but I can't read your mind.
Your output should not be possible, that is what the while loop is for. What do the two conditions return if you try them on their own?
Hang Vu
2019-5-1
Rik
2019-5-1
I don't really understand what you mean in your description. At any rate, you should be able to write some code that returns a vector with which elements are bold.
About the result you had the first point: before the first number element there is an empty cell where swapping is allowed. If you don't want that, you can put in an extra condition in the while statement:
while ~any(mod(swap_idx,2)==0) || ... %at least 1 needs to be a number
swap_idx(1)==swap_idx(2) || ... %the indices must be different
any(swap_idx==1) %the first element (1 before the first number) isn't allowed
swap_idx=valid_idx(randperm(numel(valid_idx),2));
end
Hang Vu
2019-5-1
Rik
2019-5-4
Look at the indices being swapped. What do you think is happening?
Hang Vu
2019-5-4
Rik
2019-5-4
Look at the indices. What is being swapped if they are 4 and 3?
Rik
2019-5-4
This should prevent the two swapped values to be adjacent (which swaps a value with a gap, meaning it seems the array stays the same).
while ~any(mod(swap_idx,2)==0) || ... %at least 1 needs to be a number
any(swap_idx==1) || ... %the first element (1 before the first number) isn't allowed
abs(diff(swap_idx))<=1 %the indices must be different and more than 1 appart
swap_idx=valid_idx(randperm(numel(valid_idx),2));
end
Hang Vu
2019-5-8
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