How to rearrange columns in a MATRIX?

Question

Leeba Ann Chacko 2022-9-4

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1794250-how-to-rearrange-columns-in-a-matrix

移动：Walter Roberson 2022-9-5

采纳的回答： Dyuman Joshi

I have a 2x4 matrix 'X' which looks like the follwing

X = 17.0600 29.6780 23.0660 29.4160

19.0280 42.3270 22.7940 43.0240

I would like the last 2 columns to come below the 1st 2 column so that it will look like this

X= 17.0600 29.6780

19.0280 42.3270

23.0660 29.4160

22.7940 43.0240

How do I go about this using he reshape function?

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Dyuman Joshi 2022-9-4

编辑：Dyuman Joshi 2022-9-4

在 MATLAB Online 中打开

I don't think that is possible using reshape (alone), as you are changing the order of elements. You can use vertical concatention to get the desired result -

x=[17.0600   29.6780   23.0660   29.4160;19.0280   42.3270   22.7940   43.0240];
y=[x(:,1:2);x(:,3:4)]
y = 4×2
   17.0600   29.6780
   19.0280   42.3270
   23.0660   29.4160
   22.7940   43.0240

Leeba Ann Chacko 2022-9-4

I see. The problem is that in this example, I have only 4 columns but I have an array with several martrices that have 2 rows but different column numbers. However, for all of them, I want to rearrange the matrix the way I did in the example above.

ex. x=[1 2 4 4 5 6; 3 4 6 6 7 8; 3 4 5 6 6 7;4 5 6 8 7 8]

i.e

1 2 4 4 5 6

3 4 6 6 7 8

3 4 5 6 6 7

4 5 6 8 7 8

rearranged to

1 2

3 4

4 5

4 4

6 6

5 6

6 8

5 6

7 8

6 7

7 8

I want to write a for loop to automate this for all the matrices with different column numbers. How do I write the code without specifically indicating the column numbers like you did in your solution?

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Answer 1

Dyuman Joshi 2022-9-4

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https://ww2.mathworks.cn/matlabcentral/answers/1794250-how-to-rearrange-columns-in-a-matrix#answer_1042380

移动：Walter Roberson 2022-9-5

在 MATLAB Online 中打开

x=[1 2 4 4 5 6; 3 4 6 6 7 8; 3 4 5  6 6 7;4 5 6  8 7 8];
y=[reshape(x(:,1:2:end),[],1) reshape(x(:,2:2:end),[],1)]
y = 12×2
   2
   4
   4
   5
   4
   6
   6
   8
   6
   8

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Leeba Ann Chacko 2022-9-4

移动：Walter Roberson 2022-9-5

This works perfectly, thank you!

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Answer 2

Stephen23 2022-9-4

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https://ww2.mathworks.cn/matlabcentral/answers/1794250-how-to-rearrange-columns-in-a-matrix#answer_1041430

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x = [1,2,4,4,5,6; 3,4,6,6,7,8; 3,4,5,6,6,7; 4,5,6,8,7,8]
x = 4×6
   2     4     4     5     6
   4     6     6     7     8
   4     5     6     6     7
   5     6     8     7     8
y = reshape(permute(reshape(x,size(x,1),2,[]),[1,3,2]),[],2)
y = 12×2
   2
   4
   4
   5
   4
   6
   6
   8
   6
   8

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Walter Roberson 2022-9-4

Yes, permute() is the way to go here.

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Answer 3

James Tursa 2022-9-4

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One way:

[X(:,1:2);X(:,3:4)]

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Leeba Ann Chacko 2022-9-4

Is there a way to do this without specifically indicating the column numbers like you did in your solution because I have an array with mulitple matrices containing 2 rows but different column numbers each. I cannot specify the same column numbers for all of them since I want to automate it using a for loop.

James Tursa 2022-9-4

编辑：James Tursa 2022-9-4

To receive quality answers, it is best to describe the complete problem when first posting your question. E.g., Do you want the result to always be 2 columns? Or 1/2 the original columns? Etc.

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