Split matrix into N Equal Parts by rows

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Inna Pelloso
Inna Pelloso 2022-9-3
编辑： Matt J 2024-8-16
Hi,
I have an Nx10 matrix. How can I split this into three equally sized matrices (by number of rows) ? Is this something the reshape command can handle?
Thank you!
IP

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采纳的回答

Matt J
Matt J 2022-9-3
编辑：Matt J 2022-9-3
If N is a multiple of 3, you can download blkReshape,
https://www.mathworks.com/matlabcentral/fileexchange/115340-block-transposition-permutation-and-reshaping-of-arrays
N=12; M=10;
A=reshape(1:N*M,N,M),
B=blkReshape(A,[N/3,M],1,1,[]),
A =
1 13 25 37 49 61 73 85 97 109
2 14 26 38 50 62 74 86 98 110
3 15 27 39 51 63 75 87 99 111
4 16 28 40 52 64 76 88 100 112
5 17 29 41 53 65 77 89 101 113
6 18 30 42 54 66 78 90 102 114
7 19 31 43 55 67 79 91 103 115
8 20 32 44 56 68 80 92 104 116
9 21 33 45 57 69 81 93 105 117
10 22 34 46 58 70 82 94 106 118
11 23 35 47 59 71 83 95 107 119
12 24 36 48 60 72 84 96 108 120
B(:,:,1) =
1 13 25 37 49 61 73 85 97 109
2 14 26 38 50 62 74 86 98 110
3 15 27 39 51 63 75 87 99 111
4 16 28 40 52 64 76 88 100 112
B(:,:,2) =
5 17 29 41 53 65 77 89 101 113
6 18 30 42 54 66 78 90 102 114
7 19 31 43 55 67 79 91 103 115
8 20 32 44 56 68 80 92 104 116
B(:,:,3) =
9 21 33 45 57 69 81 93 105 117
10 22 34 46 58 70 82 94 106 118
11 23 35 47 59 71 83 95 107 119
12 24 36 48 60 72 84 96 108 120
  2 个评论
Inna Pelloso
Inna Pelloso 2022-9-3
编辑：Inna Pelloso 2022-9-3
Wow! This is a seriously useful function! I wonder why there isn't a built in function like that!
Is there any way to add the last rows that are greater that the last multiple (e.g. the last two rows if I have 302 rows) to the first/middle/last block? This is a possible additional feature for this function.
Matt J
Matt J 2022-9-3
You can pad with additional rows, e.g.,
N=ceil(N/3)*3;
A(end+1:N,:)=nan;

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更多回答（2 个）

Walter Roberson
Walter Roberson 2022-9-4
pieces = 3;
N = size(A, 1);
part_sizes = floor(N/pieces) * [1 1];
part_sizes(end+1) = N - sum(part_sizes);
C = mat2cell(A, part_sizes, size(A,2));
C is now a cell array in which the rows are equally divided as possible, with the last block being shorter if necessary.
  2 个评论
Gorkem
Gorkem 2024-3-5
Thanks for the code. I was having trouble with the last block being too small compared to other blocks so I distributed residuals of the last block through the equally spaced blocks. It's not the best but here is the version I updated in this way:
pieces = 100;
N = size(A, 1);
part_sizes = floor(N/pieces) * [ones(1:pieces)];
Res = N - sum(part_sizes);
part_sizes(1:Res) = part_sizes(1:Res) + 1;
C = mat2cell(A, part_sizes, size(A,2));
AlexDiz
AlexDiz 2024-8-16
it's [ones(1, pieces)] instead of [ones(1:pieces)]
but it works perfectly !
thanks

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Matt J
Matt J 2024-8-16
编辑：Matt J 2024-8-16
Ran in:
You can also use mat2tiles,
https://www.mathworks.com/matlabcentral/fileexchange/35085-mat2tiles-divide-array-into-equal-sized-sub-arrays
which doesn't require even multiples of the block size. However, it is never advisable to use cell arrays when you don't have to.
A=rand(14,6);
B=mat2tiles(A,[4,inf]) %group every 4 rows
B = 4x1 cell array
{4x6 double} {4x6 double} {4x6 double} {2x6 double}

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