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Split matrix into N Equal Parts by rows

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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

Accepted Answer

Matt J
Matt J on 3 Sep 2022
Edited: Matt J on 3 Sep 2022
If N is a multiple of 3, you can download blkReshape,
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 Comments
Inna Pelloso
Inna Pelloso on 3 Sep 2022
Edited: Inna Pelloso on 3 Sep 2022
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 on 3 Sep 2022
You can pad with additional rows, e.g.,
N=ceil(N/3)*3;
A(end+1:N,:)=nan;

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More Answers (1)

Walter Roberson
Walter Roberson on 4 Sep 2022
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.
  1 Comment
Gorkem
Gorkem on 5 Mar 2024
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));

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