padding an array with zeros in between elements

Question

Gillean 2024-1-29

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https://ww2.mathworks.cn/matlabcentral/answers/2075621-padding-an-array-with-zeros-in-between-elements

评论： Gillean 2024-1-29

Basically, I would like to pad an array of location peak values with zeros inbetween each, the catch is the number of zeros between each should be the difference of the two ascending elements. For example, in an array A = [7 15 21 29], with a loop I would like to pad this so it turns into,

A = [ 7 0 0 0 0 0 0 0 15 0 0 0 0 0 21 0 0 0 0 0 0 0 29 ]

I'm aware I'll have to minus 1 to the equation somewhere too. As you can see, I'm basically making an ascending integer array with the elements that were not included now included as zeros... I've been trying with for loops and if statements but to no avail unfortuantely

Thanks in advance!

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Answer 1

Stephen23 2024-1-29

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编辑：Stephen23 2024-1-29

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Assuming that A is sorted, here is a simple approach:

A = [7,15,21,29];
B = A(1):A(end);
B(~ismember(B,A)) = 0
B = 1×23
     7     0     0     0     0     0     0     0    15     0     0     0     0     0    21     0     0     0     0     0     0     0    29

If A is not sorted, then replace A(1):A(end) with min(A):max(A)

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Gillean 2024-1-29

Hi, thanks a lot!! This is really nice and simple method, really appreciate it! :)

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Answer 2

Rishi 2024-1-29

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Hi Gillean,

I understand from your query that you want to modify your array such that the missing numbers between two elements are replaced by '0'.

You can preallocate an array of 0s the required size. Then, using a loop, you can calculate the number of 0s required between two elements, and shift the second element by that difference.

Here is the code to implement the same:

A = [7, 15, 21, 29];
total_length = A(end) - A(1) + 1;
% Preallocate the padded array with zeros
padded_A = zeros(1, total_length);
padded_A(1) = A(1);
insert_index = 1;
for i = 1:length(A)-1
    % Calculate the number of positions to move forward
    insert_index = insert_index + (A(i+1) - A(i));
    padded_A(insert_index) = A(i+1);
end
disp(padded_A);
     7     0     0     0     0     0     0     0    15     0     0     0     0     0    21     0     0     0     0     0     0     0    29