Exclude one row from calculation

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Max Bornemann 2019-2-22

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评论： Max Bornemann 2019-2-22

Hello, i am new in MATLAB. I am searching for a way to calculate with every but one row (in this example it is the second row).

This is my code, which doesn`t work:

Reference=2;

ABC=[1;2;3;4;5;6];

logodds(1:5,:)=log(ABC(:~=Reference,1)./ABC(Reference,1));

What i could do would be:

logodds(1:5,:)=log(ABC([1 3 4 5 6],1)./ABC(Reference,1));

But the first part of the calculation ABC([1 3 4 5 6],1) musst be dependent on "Reference" because the value of Reference can change between 1 and 6. It should be a solution, where i don´t have to enumerate every row seperately. I want to express something like: Use for calculation every row (:) except the Reference-row (~=Reference).

I will greatly appreciate any assistance.

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Answer 1

Rik 2019-2-22

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The easiest way to do this is with a logical vector:

Reference=2;
ABC=[1;2;3;4;5;6];
L=ABC~=Reference;
logodds(1:5,:)=log(ABC(L,1)./ABC(Reference,1));

However, this might fail for decimal values that have float rounding errors. In that case you may want to use ismembertol to generate the vector, or use

L= abs(ABC-Reference) < 2*eps;

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Rik 2019-2-22

You can use the all or any functions to convert L back to a vector to suit your needs. This method does not rely on the 2 being in the second row, so that does not matter.

Max Bornemann 2019-2-22