How to retrieve location values in a matrix

Question

Danish Nasir 2021-7-24

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评论： Danish Nasir 2021-7-24

Suppose i have a matrix 4x6 i.e. 6 columns and 4 rows. I want to extract different location values from the matrix i.e. 3rd location from column 1, 4th location value from column 2, 1st location value from column 3 etc. ([ 3 4 1 5 2 2]). Then i have to add these column location values. Pls suggest the code.

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Answer 1

Chunru 2021-7-24

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% Generate a 4X6 matrix
a = randi(10, 4, 6)
a = 4×6
     7     6     6     8     8     6
     5     6     4     7     5     8
     2     8     6     7     1     1
     2     6     9     3     6     6
% The index to each column
%idx = [ 3 4 1 5 2 2]       % 5 is not correct
idx = [ 3 4 1 4 2 2];
% Fund the corresponding linear index
ii = sub2ind([4, 6], idx, 1:6);
% Show the extracted data
a(ii)
ans = 1×6
     2     6     6     3     5     8
sum(a(ii))
ans = 30

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Danish Nasir 2021-7-24

Actually i want to take indices of matrix a (4x6), and want to extract the values of some other matrix b (4x6) of same size with these indices.

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Answer 2

Sulaymon Eshkabilov 2021-7-24

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https://ww2.mathworks.cn/matlabcentral/answers/884814-how-to-retrieve-location-values-in-a-matrix#answer_752824

% e.g.:
A = randi([0, 13], 4,6)
A = 4×6
     8    12     8     6    10     4
     9     2     1     3     7     1
     2     6     5     5     0     1
     3     3    10    10     9     1
A(3,1), A(4, 2), A(1,3)
ans = 2
ans = 3
ans = 8