Link the 2th column of a matrix to the first depending on another matrix.

Question

Klaas 2015-2-9

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/176743-link-the-2th-column-of-a-matrix-to-the-first-depending-on-another-matrix

关闭： MATLAB Answer Bot 2021-8-20

在 MATLAB Online 中打开

Hello,

I'll just give a simple example to show what I want:

I have a matrix

A=[1,4;
   2,5;
   3,6];

And a long vector B with values 1,2 and 3 in an undefined order.

B = [1;3;1;2;1;3...];

From A and B I want to make one matrix C in which the first column is vector B and for the second column I want to let the values depend of the value of B. So if the value of B is 1 I want to get a 4, if 2 I want 5, if 3 I want to get 6. So each time the according value defined in matrix A.

Thanks in advance!

2 个评论
显示无隐藏无

Image Analyst 2015-2-9

You left the answer C out of your example for some reason.

Klaas 2015-2-10

C should be: [1,4;3,6;1,4;2,5;1,4;3,6;...]

此问题已关闭。

Answer 1

Image Analyst 2015-2-9

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/176743-link-the-2th-column-of-a-matrix-to-the-first-depending-on-another-matrix#answer_167463

在 MATLAB Online 中打开

How about this:

A=[1,4;
   2,5;
   3,6];
B = [1;3;1;2;1;3];
C = [B, A(B,2)]
C =
     1     4
     3     6
     1     4
     2     5
     1     4
     3     6

3 个评论
显示 1更早的评论隐藏 1更早的评论

Klaas 2015-2-10

编辑：Klaas 2015-2-10

I still have a problem. This works for my example but in my script the numbers 1,2 and 3 from the example are decimal fraction. So I always get the 'Subscript indices must either be real positive integers or logicals.' error.

Someone who has a different solution?

Image Analyst 2015-2-10

Let's say the number is 2.37. So you want row #2.37 from A. Can you explain exactly what it means to you to get the 2.37'th row from the second column of A?

Answer 2

Roger Stafford 2015-2-10

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/176743-link-the-2th-column-of-a-matrix-to-the-first-depending-on-another-matrix#answer_167630

在 MATLAB Online 中打开

Perhaps what you need is

[~,ix] = ismember(B,A(:,1));
C = A(ix,:);

This assumes that every value in B is to be found somewhere in the first column of A. If not, you will receive an error message.

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Image Analyst 2015-2-10

Oh, is that what he meant? I thought the B was the row numbers of A that he wanted to extract. I guess it's ambiguous but you might be right. Of course having the first column of A be row numbers didn't help clarify it, in fact it made it more ambiguous.