Is equality == available in Matlab 2017 ?

Question

JGUIS 2018-8-21

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回答： Chad Greene 2018-8-21

Hello, I use Matlab 2017 R2017b and I would like to establish an equality of two vectors of this kind :

if true
A = [1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4];
B = [1 1 1 2 2 2 3 3 3 4 4 4];
A == B  
end

I would like to obtain a vector as result but ''=='' is not recognize. Is equality not exist in Matlab version 2017? If yes, how can I exactly replace that to have the same result that furnished ''==''

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Stephen23 2018-8-21

编辑：Stephen23 2018-8-21

"Is equality not exist in Matlab version 2017"

== exists for all MATLAB versions since atleast the first PC version of 1985.

"I would like to obtain a vector as result but ''=='' is not recognize."

You don't define what "equality" means for vectors of two different sizes. What size do you expect the output vector to be?

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Answer 1

Geoff Hayes 2018-8-21

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JGUIS - equality does exist in MATLAB, see Determine equality for details. With your above example, you are probably observing the

 Error using  == 
 Matrix dimensions must agree.

error because your two arrays are of different dimensions and so cannot possibly be equal.

I suspect that you are looking for a different type of equality (perhaps they have the same elements, same order, etc.). Please clarify.

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ARN 2018-8-21

Matrix dimensions should be equal to use this operator and i am using "==" in Matlab 2017 and its working. Make sure the two vectors/matrices you are comparing must be of same size. You can also see isequal if it fits in your code

JGUI 2018-8-21

在 MATLAB Online 中打开

Thank a lot for your answer, In fact, it was an error of inattention about the size of the matrix I try this and I obtain what i was looking for : a binary vector 1x19

if true
W = [1 1 1 1 1 2 2 2 2 3 3 3 3 3 4 4 4 4 4];
 for i = 1 : 4
        wx_ind = W == i;
 end

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Answer 2

Steven Lord 2018-8-21

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I'm fairly certain the == operator has been part of MATLAB since Cleve's original version. [If not, it was introduced not long after that.] It is certainly present in release R2017b. The problem you receive is not that == is undefined, it's that you're trying to compare arrays of different sizes.

If you wanted a matrix as a result, with a number of rows equal to the number of elements in A and a number of columns equal to the number of elements in B, that's possible thanks to implicit expansion.

A = [1 2 3 4];
B = [3 1];
A.' == B

If you wanted to know if the elements in A are present in B or vice versa, take a look at the ismember function.

If neither of those are what you want, please explain in more detail what you expect the result of A == B to be (what size should it be?) and how you would compute it by hand and we may be able to help you determine how to compute it in MATLAB.