CODEWITHSUNDEEP
matlabmatrixoctave
Rgwan
Rgwan

Reputation: 50

matrix indexing with another matrix returning "subscript indices must be either positive integers or logicals"

Trying to understand matrix indexing.

A = [2 3 0 0 5; 3 0 0 0 0];
B = [1 1 0 0 1; 1 0 0 0 0];

When I run

A(1, B(1, :))

I was expecting 

[2 3 5]

But instead, I get the error:

error: subscript indices must be either positive integers or logicals.

Upvotes: 0

Views: 60

Answers (1)

chappjc
chappjc

Reputation: 30579

Convert to logical:

>> A(1, logical(B(1, :)))
ans =
     2     3     5

Since B is actually a double array, it thinks you are trying to index element 0, which causes the error.

Or, if you prefer double negation, do A(1, ~~B(1, :)). Personally, I think that looks ugly. Or simply test: A(1, B(1, :)==1), A(1, B(1, :)~=0), A(1, B(1, :)>0), etc.

The other solution is to use find to satisfy the "positive integers" part of the error:

>> A(1, find(B(1, :)))
ans =
     2     3     5

Upvotes: 2

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