Delete last n1,n2,n3 (...) elements in each row in a Matrix in an efficient way or set to zero

Question

Tim 2014-2-21

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https://ww2.mathworks.cn/matlabcentral/answers/117152-delete-last-n1-n2-n3-elements-in-each-row-in-a-matrix-in-an-efficient-way-or-set-to-zero

回答： Roger Stafford 2014-2-22

I've a large set of data and i want to remove from the end of each row a different amount of elements (0-n). Is there a fast way to do this without using a loop?

As an example: A= % In reality different numbers, not only ones!

   1     1     1     1
   1     1     1     1
   1     1     1     1
   1     1     1     1
   1     1     1     1

Then I've a vector saying how many elements to delete from each row, e.g.:

B =

1 3 0 2 1

So the result would look like:

A2

   1     1     1     0
   1     0     0     0
   1     1     1     1
   1     1     0     0
   1     1     1     0

Thanks so much in advance!

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Answer 1

Roger Stafford 2014-2-22

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在 MATLAB Online 中打开

 [m,n] = size(A);
 p = cumsum(accumarray([(1:m)',n+1-B'],1,[m,n+1]),2);
 A(p(:,1:n)==1) = 0;

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Answer 2

Image Analyst 2014-2-21

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https://ww2.mathworks.cn/matlabcentral/answers/117152-delete-last-n1-n2-n3-elements-in-each-row-in-a-matrix-in-an-efficient-way-or-set-to-zero#answer_125324

在 MATLAB Online 中打开

As long as you want to simply set to zero, no need to use cell arrays:

A=[...
     1     1     1     1     1
     1     1     1     1     1
     1     1     1     1     1
     1     1     1     1     1
     1     1     1     1     1]
B =[1     3     0     2     1];
for row = 1 : size(A, 2)
  A(row,(end-B(row)+1):end) = 0;
end
A % Print to command window.