Insert zeros in random positions following another zero

Question

Phillip 2023-11-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2053002-insert-zeros-in-random-positions-following-another-zero

评论： Phillip 2023-11-28

Hi All,

I have a large array such as this one: X = [2 1 0 4 5 0 778 90 0 3 88 0 77 66 0 12 23 0 45 80 0 89 67 0 34 67 0 76 32 0]; (just much larger)

I'd like to insert 20% of additional zeros at random positions following another 0 such as:

new_X = [2 1 0 0 4 5 0 778 90 0 3 88 0 77 66 0 12 23 0 0 45 80 0 89 67 0 34 67 0 76 32 0];

I need to find the indeces of the zeros in X but then I can't get the "random" 20% of zeros correct...

Does anybody know how to do that?

Kind regards

Phil

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Phillip 2023-11-28

% This does what I want...but do you know of a quicker way?

X = [2 1 0 4 5 0 778 90 0 3 88 0 77 66 0 12 23 0 45 80 0 89 67 0 34 67 0 76 32 0];

% Find indices of zeros in X

zero_indices = find(X == 0);

% Calculate additional 0s to insert (20% of the total number of 0 in X)

num_existing_zeros = length(zero_indices);

num_additional_zeros = round(0.2 * num_existing_zeros);

% Randomly select positions following existing 0s

additional_zero_positions = randsample(num_existing_zeros, num_additional_zeros);

% Sort 'em

additional_zero_positions = sort(additional_zero_positions);

% Insert 0s

for i = 1:num_additional_zeros

insert_index = zero_indices(additional_zero_positions(i)) + i;

X = [X(1:insert_index+1) 0 X(insert_index+2:end)];

zero_indices = zero_indices + 1;

end

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Answer 1

Steven Lord 2023-11-28

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2053002-insert-zeros-in-random-positions-following-another-zero#answer_1361647

在 MATLAB Online 中打开

You can use repelem to replicate the elements.

X = [2 1 0 4 5 0 778 90 0 3 88 0 77 66 0 12 23 0 45 80 0 89 67 0 34 67 0 76 32 0];

Start off by "replicating" every element once.

replicationFactor = ones(size(X));

Identify where the zero elements are located.

iszero = X == 0;
zeroLocations = find(iszero)
zeroLocations = 1×10
     3     6     9    12    15    18    21    24    27    30
numZeros = numel(zeroLocations)
numZeros = 10

Let's select 20% of the 0 locations (rounded up) to replicate twice. To do this, update the selected element in replicationFactor from 1 to 2.

elementsInZeroLocationsToReplicate = randperm(numZeros, ceil(0.2*numZeros));
randomSelection = zeroLocations(elementsInZeroLocationsToReplicate)
randomSelection = 1×2
     6    15
replicationFactor(randomSelection) = 2
replicationFactor = 1×30
     1     1     1     1     1     2     1     1     1     1     1     1     1     1     2     1     1     1     1     1     1     1     1     1     1     1     1     1     1     1

Now replicate with repelem.

Y = repelem(X, replicationFactor)
Y = 1×32
     2     1     0     4     5     0     0   778    90     0     3    88     0    77    66     0     0    12    23     0    45    80     0    89    67     0    34    67     0    76

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Phillip 2023-11-28

Thank you!!!

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Answer 2

Davide Masiello 2023-11-28

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2053002-insert-zeros-in-random-positions-following-another-zero#answer_1361612

编辑：Davide Masiello 2023-11-28

在 MATLAB Online 中打开

This should work without the need for a for loop.

X = [2 1 0 4 5 0 778 90 0 3 88 0 77 66 0 12 23 0 45 80 0 89 67 0 34 67 0 76 32 0];

Select two random locations and increase the index by one (i.e. the new zero goes after the old random zero).

idx = sort(randsample(find(X==0),2));
idx = idx+[1:length(idx)]
idx = 1×2
     4    32

Create a new vector of NaNs of the length required for the new vector.

newX = nan(1,length(X)+length(idx));

First place the new additional zeros.

newX(idx) = 0;

Then add the old vector where the NaNs are left.

newX(isnan(newX)) = X;

See the result below

disp(newX)
     2     1     0     0     4     5     0   778    90     0     3    88     0    77    66     0    12    23     0    45    80     0    89    67     0    34    67     0    76    32     0     0