CODEWITHSUNDEEP
matlabmatrix
Guillaume
Guillaume

Reputation: 123

How to compare two matrices?

My goal is to compare two matrices: A and B in two different files:

 function [Result]=test()
     A_Mat= load('fileA', 'A')
     B_Mat= load('fileB', 'B')
     Result= A_Mat == B_Mat
  end

The result that I want is a matrix that includes the difference between A and B.

The error that I have is: 

error: binary operator '==' not implemented for 'scalar struct' by 'scalar struct' operations

Upvotes: 1

Views: 3016

Answers (4)

Israel Unterman
Israel Unterman

Reputation: 13520

First, the operator == does work on matrices, and it returns a logical matrix of true/false (1/0) where the corresponding items are equal or different respectively. From the error you got it seems that you didn't read matrices from the file, but structs, and indeed, == doesn't work for structs.

You can use isequal for both structs and matrices. This function returns only one value - 1 or 0 (true/false).

ADDED

After seeing @dasdingonesin answer, who actually pointed to the exact problem, I just wanted to add that when you write

A_Mat= load('fileA', 'A')

it returns a struct as with the field A.

So:

A_Mat = s.A

Upvotes: 0

Adriaan
Adriaan

Reputation: 18207

If you simply want the difference between A and B you should first use load as dasdingonesin suggested, and either check for full matrix equality with isequal or elementwise equality with ==. The difference, however, is simply given by - of course:

isequal(A,B); % returns a boolean for full matrix equality
A==B;         % returns a logical matrix with element wise equality
A-B;          % returns a matrix with differences between the two matrices

Do note that isequal can deal with matrices of unequal size (it will simply return 0), whilst both == and - will crash with the error Matrix dimensions must agree.

Upvotes: 0

romulus001
romulus001

Reputation: 318

Use the isequal function.

isequal(A,B)

Upvotes: 4

dasdingonesin
dasdingonesin

Reputation: 1358

The load function doesn't return what you think it returns. Reading the extensive and easily comprehensible MATLAB documentation always helps.

function Result=test()
  load('fileA', 'A');
  load('fileB', 'B');
  Result = A == B
end

Upvotes: 6

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