How to replace every value with the index of the value to the left of it

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sunny blue 2021-10-10

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https://ww2.mathworks.cn/matlabcentral/answers/1486791-how-to-replace-every-value-with-the-index-of-the-value-to-the-left-of-it

评论： sunny blue 2021-10-10

This way the left most column is 0. I initially tried using a while loop but with a really big matrix, it takes way too long. so if I had a matrix

x= [ 2 3  4  5  6 ; 
     8 9 10 11 12 ] 

the matrix i would want is

[ 0 1 3 5 7  9; 
  0 2 4 6 8 10 ]

I'm kind of at a crossroads here.

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回答（1 个）

DGM 2021-10-10

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https://ww2.mathworks.cn/matlabcentral/answers/1486791-how-to-replace-every-value-with-the-index-of-the-value-to-the-left-of-it#answer_805281

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There's this:

x = [ 2 3 4 5 6 ; 8 9 10 11 12 ]
x = 2×5
     2     3     4     5     6
     8     9    10    11    12
idx = reshape(1:numel(x),size(x));
out = [zeros(size(x,1),1) idx(:,1:end-1)]
out = 2×5
     0     1     3     5     7
     0     2     4     6     8