How to access specific elements of an array?

Question

Karthik Nagarajan 2017-7-14

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/348743-how-to-access-specific-elements-of-an-array

评论： Star Strider 2017-7-14

采纳的回答： Star Strider

在 MATLAB Online 中打开

Suppose I have two matrices A and x as follows:

x =

     1     2
     2     3

A =

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

Each row of x contains the row and column indices of an element of A that I would like to access and change. In the above example, I want to change the (1,2) and (2,3) elements of A. Suppose I want to set the value of these elements to 5. The command 'A([1 2],[2 3]) = 5;' produces A =

   5     5     1
   5     5     1
   1     1     1
   1     1     1

However, what I want is the following:

A =

   5     1     1
   1     5     1
   1     1     1
   1     1     1

In my actual code, A and x may have thousands of elements each. Therefore, I am wondering whether it is possible to do this without using a for loop?

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Answer 1

Star Strider 2017-7-14

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/348743-how-to-access-specific-elements-of-an-array#answer_274160

编辑：Star Strider 2017-7-14

在 MATLAB Online 中打开

One approach:

ix = sub2ind(size(A), x(:,1), x(:,2));              % Change Subscripts To Linear Index Vector
A(ix) = 5;
A =
     1     5     1     1
     1     1     5     1
     1     1     1     1
     1     1     1     1