CODEWITHSUNDEEP
matlabmatrixindexing
Uri Cohen
Uri Cohen

Reputation: 3608

Accessing a data matrix using indices stored at another matrix

In matlab, I commonly have a data matrix of size NxMxLxK which I wish to index along specific dimension (e.g. the forth) using an indices matrix of size NxMxL with values 1..K (assume the are all in this range):

>>> size(Data)
ans =
     7    22    128    40
>>> size(Ind)
ans =
     7    22    128

I would like to have code without loops which achieve the following effect:

Result(i,j,k) = Data(i,j,k,Ind(i,j,k))

for all values of i,j,k in range.

Upvotes: 0

Views: 59

Answers (1)

Adiel
Adiel

Reputation: 3071

You can vectorize your matrices and use sub2ind :

% create indices that running on all of the options for the first three dimensions:
A = kron([1:7],ones(1,22*128));
B = repmat(kron([1:22],ones(1,128)),1,7);
C = repmat([1:128],1,7*22);

Result_vec = Data(sub2ind(size(Data),A,B,C,Ind(:)'));
Result = reshape(Result_vec,7,22,128);

Upvotes: 3

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