How to cut an array and reshape it while keeping the content in order?

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Joseph Schmidt 2016-7-5

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回答： Jos (10584) 2016-7-6

I have an array similar to what's below. How do I cut and move it so that after the 11th column (were it begins to go to 1 again) so that it's a 10x11 matrix instead of 5x22?

The reshape function doesn't work as it keeps the 1st column, pushes the 2nd column down and below the 1st column, keeps the 3rd column, and pushes the 4th column below the 2nd column. It messes up the data. Basically I want to cut the latter half of the data from column 12:end and place it below the 1:11 columns.

(5x22) T1 =

   1     1     1     1     1     1     1     0     0     0     1     1     1     1     1     1     1     1     0     0     0
   1     1     1     1     1     1     0     0     0     0     1     1     1     1     1     1     1     0     0     0     0
   1     1     1     1     1     1     1     1     1     0     1     1     1     1     1     1     1     1     1     1     0
   1     1     1     1     0     0     0     0     0     0     1     1     1     1     1     0     0     0     0     0     0
   1     1     1     1     1     1     1     1     1     0     1     1     1     1     1     1     1     1     1     1     0

(10x11)T1 =

   1     1     1     1     1     1     1     0     0     0
   1     1     1     1     1     1     0     0     0     0
   1     1     1     1     1     1     1     1     1     0
   1     1     1     1     0     0     0     0     0     0
   1     1     1     1     1     1     1     1     1     0
   1     1     1     1     1     1     1     0     0     0
   1     1     1     1     1     1     0     0     0     0
   1     1     1     1     1     1     1     1     1     0
   1     1     1     1     0     0     0     0     0     0
   1     1     1     1     1     1     1     1     1     0

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Answer 1

Star Strider 2016-7-5

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This is how I would do it:

T1 = [T1(:,1:11); T1(:,12:end)]

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Joseph Schmidt 2016-7-5

Do you know if there's a way to do this for an arbitrary sized matrix? I'm going to change the size of the original T1 to be a whole range of sizes. Say T1 is size 10x42 and I want to make it into size 20x21. I want a way to have it be reshaped but without me having to specify it each time.

Thank you, Joseph Schmidt

Star Strider 2016-7-5

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My pleasure.

The easiest way is to use the size function to define the column length.

This works with your ‘T1’ matrix, and should work for the others:

T1 = [T1(:,1:fix(size(T1,2)/2)); T1(:,fix(size(T1,2)/2)+1:end)]

The fix call may not be absolutely necessary, but I always include it to prevent problems.

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Answer 2

James Tursa 2016-7-5

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result = [T1(:,1:11);T1(:,12:22)];

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Joseph Schmidt 2016-7-5

Do you know if there's a way to do this for an arbitrary sized matrix? I'm going to change the size of the original T1 to be a whole range of sizes. Say T1 is size 10x42 and I want to make it into size 20x21. I want a way to have it be reshaped but without me having to specify it each time.

Thank you, Joseph Schmidt

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Answer 3

Stephen23 2016-7-6

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编辑：Stephen23 2016-7-6

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This code can easily be changed to split the matrix into two, three, or more blocks. It assumes that the number of columns is divisible by this number of blocks.

>> blk = 2;
>> tmp = reshape(T1,size(T1,1),[],blk);
>> reshape(permute(tmp,[1,3,2]),[],size(tmp,2))
ans =
   1     1     1     1     1     1     1     0     0     0
   1     1     1     1     1     1     0     0     0     0
   1     1     1     1     1     1     1     1     1     0
   1     1     1     1     0     0     0     0     0     0
   1     1     1     1     1     1     1     1     1     0
   1     1     1     1     1     1     1     0     0     0
   1     1     1     1     1     1     0     0     0     0
   1     1     1     1     1     1     1     1     1     0
   1     1     1     1     0     0     0     0     0     0
   1     1     1     1     1     1     1     1     1     0

Example

We first define a function:

function out = moveblock(mat,blk)
tmp = reshape(mat,size(mat,1),[],blk);
out = reshape(permute(tmp,[1,3,2]),[],size(tmp,2));
end

and test this on a matrix:

>> T = ones(3,1)*(1:12)
T =
  2    3    4    5    6    7    8    9   10   11   12
  2    3    4    5    6    7    8    9   10   11   12
  2    3    4    5    6    7    8    9   10   11   12
>> moveblock(T,2)
ans =
  2    3    4    5    6
  2    3    4    5    6
  2    3    4    5    6
  8    9   10   11   12
  8    9   10   11   12
  8    9   10   11   12
>> moveblock(T,3)
ans =
  2    3    4
  2    3    4
  2    3    4
  6    7    8
  6    7    8
  6    7    8
 10   11   12
 10   11   12
 10   11   12
>> moveblock(T,4)
ans =
  2    3
  2    3
  2    3
  5    6
  5    6
  5    6
  8    9
  8    9
  8    9
 11   12
 11   12
 11   12

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Answer 4

Jos (10584) 2016-7-6

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This is easy using a cell array as an intermediate step

    T = repmat(1:12,3,1) % example array
    S = size(T) 
    n = 3 
    if mod(S(2),n)>0
       C = mat2cell(T, S(1), repmat(S(2)/n,1,n)) 
       Tout = cat(1,C{:})
    else
       disp('Not possible.')
       Tout = [] 
    end