eliminate several columns and rows of a matrix using vectors.

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Pedro Guevara 2019-5-9

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https://ww2.mathworks.cn/matlabcentral/answers/461216-eliminate-several-columns-and-rows-of-a-matrix-using-vectors

评论： Pedro Guevara 2019-5-9

Good afternoon. Request your help with the following problem. I have a matrix called "Cons" - you can see it in the image -, and I have 2 vectors [Ii2, Ji2] that contain the position of rows and columns that I want to eliminate from the "Cons" matrix. For example, I want to eliminate the first 3 columns of "Cons" according to the value of the vector Ji2. How do I remove those columas and those same rows from my "Cons" matrix? Thank you.

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Answer 1

per isakson 2019-5-9

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https://ww2.mathworks.cn/matlabcentral/answers/461216-eliminate-several-columns-and-rows-of-a-matrix-using-vectors#answer_374326

编辑：per isakson 2019-5-9

在 MATLAB Online 中打开

Try

>> m = magic( 5 )
m =
    17    24     1     8    15
    23     5     7    14    16
     4     6    13    20    22
    10    12    19    21     3
    11    18    25     2     9
% eliminate column 1,2 and 3    
>> m(:,1:3)=[]
m =
     8    15
    14    16
    20    22
    21     3
     2     9
>> m([4,5],:)=[]
% eliminate row 4 and 5
m =
     8    15
    14    16
    20    22
>> 
>> m = magic(5);
>> cols_to_eliminate = [1,3,5];
>> m(:,cols_to_eliminate) = []
m =
    24     8
     5    14
     6    20
    12    21
    18     2
>> 
>> m = magic(5);
>> cols_to_eliminate = [1,3,5];
>> rows_to_eliminate = [2,4];
>> m(rows_to_eliminate,cols_to_eliminate) = []
A null assignment can have only one non-colon index. 

That doesn't work, but

>> rows_to_keep = [2,4];
>> cols_to_keep = [1,3,5];
>> m = magic(5);
>> m = m(rows_to_keep,cols_to_keep)
m =
    23     7    16
    10    19     3
>> 