extract all rows of a matrix except 'r' (vector) rows

Question

Alberto Acri 2023-9-8

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2018506-extract-all-rows-of-a-matrix-except-r-vector-rows

回答： MarKf 2023-9-8

Hi! I need to extract all rows of 'matrix' except 'r' rows.

matrix = [54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65];
r = [1; 2; 3; 4: 9];

The result is:

matrix_out = [58; 59; 60; 61; 63; 64; 65];

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Answer 1

Stephen23 2023-9-8

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https://ww2.mathworks.cn/matlabcentral/answers/2018506-extract-all-rows-of-a-matrix-except-r-vector-rows#answer_1305456

在 MATLAB Online 中打开

The most efficient approach:

matrix = [54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65];
r = [1; 2; 3; 4; 9];
matrix_out = matrix;
matrix_out(r) = []
matrix_out = 7×1
    58
    59
    60
    61
    63
    64
    65

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Answer 2

Dyuman Joshi 2023-9-8

2
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https://ww2.mathworks.cn/matlabcentral/answers/2018506-extract-all-rows-of-a-matrix-except-r-vector-rows#answer_1305451

编辑：Dyuman Joshi 2023-9-8

在 MATLAB Online 中打开

matrix = [54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65];
r = [1; 2; 3; 4; 9];
%Method 1
%remove directly
matrix(r,:)=[];
%or
%Method 2
%remove indirectly
idx = 1:size(matrix,1);
ix = setdiff(idx,r);
matrix = matrix(ix,:);

Note that Method 1 won't work when there is an index not in the range of the dimensions of the array matrix.

For such cases, use Method 2.

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Answer 3

MarKf 2023-9-8

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2018506-extract-all-rows-of-a-matrix-except-r-vector-rows#answer_1305476

在 MATLAB Online 中打开

mat = magic(8)
mat = 8×8
    64     2     3    61    60     6     7    57
     9    55    54    12    13    51    50    16
    17    47    46    20    21    43    42    24
    40    26    27    37    36    30    31    33
    32    34    35    29    28    38    39    25
    41    23    22    44    45    19    18    48
    49    15    14    52    53    11    10    56
     8    58    59     5     4    62    63     1
r_not = [1 3:5 8];
mat(r_not,:) = [] %use mat_o = mat; to keep the original mat;  
mat = 3×8
     9    55    54    12    13    51    50    16
    41    23    22    44    45    19    18    48
    49    15    14    52    53    11    10    56

There are some issues with your example:

matrix = [54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65];
r = [1:3, 6, 9]; %btw this did not work with those dimensions; 
% also not the way you wanted with those indices (matrix_out just removed 1:3)
matrix_out = matrix; 
matrix_out(r,:) = [] 
matrix_out = 7×1
    57
    58
    60
    61
    63
    64
    65