Use an array containing indexes to extract a subset of larger array

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Scorp 2022-7-15

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1760460-use-an-array-containing-indexes-to-extract-a-subset-of-larger-array

评论： Jeffrey Clark 2022-7-15

采纳的回答： Voss

largeArray = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]

indexes = [5,9,16]

% use the indexes array to extract 3 elements at each index in the largeArray to yield:

subSetArray = [5,6,7 ; 9,10,11; 16,17,18]

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Jeffrey Clark 2022-7-15

在 MATLAB Online 中打开

@Scorp, attack problems like this by looking at what you have and then what you want. I won't give you the answer here:

>>largeArray = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
largeArray =
  Columns 1 through 17
     1     2     3     4     5     6     7     8     9    10    11    12    13    14    15    16    17
  Columns 18 through 20
    18    19    20
    
>>indexes = [5,9,16]
indexes =
     5     9    16
>>subSetArray = [5,6,7 ; 9,10,11; 16,17,18]
subSetArray =
     5     6     7
     9    10    11
    16    17    18
    
>>note = indexes' % apostrophy converts arrays (look it up)
note =
     5
     9
    16
    
>>also = 2+indexes' % compare with subSetArray
also =
     7
    11
    18

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Answer 1

Voss 2022-7-15

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1760460-use-an-array-containing-indexes-to-extract-a-subset-of-larger-array#answer_1007815

在 MATLAB Online 中打开

largeArray = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
largeArray = 1×20
     1     2     3     4     5     6     7     8     9    10    11    12    13    14    15    16    17    18    19    20
indexes = [5,9,16]
indexes = 1×3
     5     9    16
% use the indexes array to extract 3 elements at each index in the largeArray to yield:
% subSetArray = [5,6,7 ; 9,10,11; 16,17,18]
subSetArray = largeArray(indexes(:)+(0:2))
subSetArray = 3×3
     5     6     7
     9    10    11
    16    17    18

Make sure you don't go off the end of largeArray:

indexes = [5,9,19]
indexes = 1×3
     5     9    19
subSetArray = largeArray(indexes(:)+(0:2))
Index exceeds the number of array elements. Index must not exceed 20.