How to construct a matrix values by its row or column indexes?

Question

Antonio Trujillo-Ortiz 2013-7-9

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/81585-how-to-construct-a-matrix-values-by-its-row-or-column-indexes

Hi all,

I need your help on this. Suppose we have a 4x3 matrix and we need to construct a metrix with its row and column indexes as follows,

R = 1 1 1; 2 2 2; 3 3 3; 4 4 4

C= 1 2 3; 1 2 3; 1 2 3; 1 2 3

Thx in advance.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Evan 2013-7-9

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/81585-how-to-construct-a-matrix-values-by-its-row-or-column-indexes#answer_91289

编辑：Evan 2013-7-9

在 MATLAB Online 中打开

A(sub2ind(size(A),R,C))

Example:

>>A = magic(4);
>>R = [1 1 1; 2 2 2; 3 3 3; 4 4 4];
>>C = [1 2 3; 1 2 3; 1 2 3; 1 2 3];
>>B = A(sub2ind(size(A),R,C))
B =
    16     2     3
     5    11    10
     9     7     6
     4    14    15

If you're not talking about a generalized case and just want that particular indexing of any matrix, though, it looks like you just need to trim off part of the matrix:

>>B = A(1:4,1:3);
B =
    16     2     3
     5    11    10
     9     7     6
     4    14    15

2 个评论
显示无隐藏无

Antonio Trujillo-Ortiz 2013-7-9

Hi Evan,

What I need is to get from any matrix, two new ones with its row and column indexes. I mean,

Eg, given

A = [2 5 6;12 7 0;2 9 7;4 17 1 0]

we have 4 rows and 3 columns, and we need to get matrices

R = [1 1 1;2 2 2;3 3 3;4 4 4]

and

C = [1 2 3;1 2 3;1 2 3;1 2 3]

Thx

Evan 2013-7-9

编辑：Evan 2013-7-9

Ah, okay. So the row and column indices of every element in your array? I have submitted a new answer below that does this. Note that it looks like your example is for a 3x4 matrix, though, not a 4x3.

请先登录，再进行评论。