Extract a series of values every n row of a matrix

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Silvia Marchesi 2022-6-14

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评论： Silvia Marchesi 2022-6-14

Hello, I have a matrix with the following dimensions 154353x3.

I would need to extract 2180 rows every 2580 rows (that means that I 2180 rows that I need to analyze, then 399 rows I do not need to analyze, then another 2180 rows I need to analyze and so on).

How is the most effective way to extract only the segments I have to analyze?

Thank you for your help

Silvia

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Dyuman Joshi 2022-6-14

How are the 2180 rows selected? Serially? Randomly? Any particular pattern?

Silvia Marchesi 2022-6-14

Serially, 2180 to analyze, then 399 to not analyze, then 2180 to analyze and so on...

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Answer 1

DGM 2022-6-14

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https://ww2.mathworks.cn/matlabcentral/answers/1739910-extract-a-series-of-values-every-n-row-of-a-matrix#answer_985200

在 MATLAB Online 中打开

Consider the small example:

% a small 100x3 test array
A = repmat((1:100).',[1 3])
A = 100×3
   1     1
   2     2
   3     3
   4     4
   5     5
   6     6
   7     7
   8     8
   9     9
  10    10
% parameters
blocksize = 10;
rowstokeep = 7;
% reshape and truncate
A = reshape(permute(A,[1 3 2]),blocksize,[],3);
A = permute(A(1:rowstokeep,:,:),[1 3 2])
A = 
A(:,:,1) =

   1     1
   2     2
   3     3
   4     4
   5     5
   6     6
   7     7


A(:,:,2) =

  11    11
  12    12
  13    13
  14    14
  15    15
  16    16
  17    17


A(:,:,3) =

  21    21
  22    22
  23    23
  24    24
  25    25
  26    26
  27    27


A(:,:,4) =

  31    31
  32    32
  33    33
  34    34
  35    35
  36    36
  37    37


A(:,:,5) =

  41    41
  42    42
  43    43
  44    44
  45    45
  46    46
  47    47


A(:,:,6) =

  51    51
  52    52
  53    53
  54    54
  55    55
  56    56
  57    57


A(:,:,7) =

  61    61
  62    62
  63    63
  64    64
  65    65
  66    66
  67    67


A(:,:,8) =

  71    71
  72    72
  73    73
  74    74
  75    75
  76    76
  77    77


A(:,:,9) =

  81    81
  82    82
  83    83
  84    84
  85    85
  86    86
  87    87


A(:,:,10) =

  91    91
  92    92
  93    93
  94    94
  95    95
  96    96
  97    97