locate within the first column of a matrix a sequence of numbers and extract those rows

hi! I have the matrix 'M'. How can I locate inside the first column of the matrix 'M' the sequence of numbers (1 to #) and extract those rows?

For example, this matrix 'M' breaks down into:

• rows 1:9
• rows 10:12
• rows 13:18

Answer 1

[Stephen23]

Use DIFF, which is a key MATLAB function.

M = load('M.mat').M

M = 18x5

1.0000 -0.0394 -0.0204 0.0590 0 2.0000 -0.0429 -0.0225 0.0593 0 3.0000 -0.0398 -0.0201 0.0591 0 4.0000 -0.0431 -0.0224 0.0593 0 5.0000 -0.0400 -0.0200 0.0591 0 6.0000 -0.0431 -0.0223 0.0593 0 7.0000 -0.0399 -0.0202 0.0591 0 8.0000 -0.0398 -0.0203 0.0591 0 9.0000 -0.0401 -0.0200 0.0591 0 1.0000 -0.0376 -0.0140 0.0172 0

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X = diff([0;find(diff([M(:,1);0])<0)]);
Y = size(M,2);
C = mat2cell(M,X,Y)

C = 3x1 cell array
    {9x5 double}
    {3x5 double}
    {6x5 double}

Checking the content:

C{:}

ans = 9x5

1.0000 -0.0394 -0.0204 0.0590 0 2.0000 -0.0429 -0.0225 0.0593 0 3.0000 -0.0398 -0.0201 0.0591 0 4.0000 -0.0431 -0.0224 0.0593 0 5.0000 -0.0400 -0.0200 0.0591 0 6.0000 -0.0431 -0.0223 0.0593 0 7.0000 -0.0399 -0.0202 0.0591 0 8.0000 -0.0398 -0.0203 0.0591 0 9.0000 -0.0401 -0.0200 0.0591 0

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ans = 3x5

1.0000 -0.0376 -0.0140 0.0172 0 2.0000 -0.0374 -0.0168 0.0167 0 3.0000 -0.0341 -0.0151 0.0177 0

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ans = 6x5

1.0000 -0.0441 -0.0161 0.0761 0 2.0000 -0.0408 -0.0243 0.0753 0 3.0000 -0.0426 -0.0155 0.0761 0 4.0000 -0.0422 -0.0146 0.0761 0 5.0000 -0.0443 -0.0151 0.0762 0 6.0000 -0.0444 -0.0150 0.0762 0

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