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Comparing two Matrix for similar elements

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Nikita Johnson
Nikita Johnson 2017-5-24
评论： Walter Roberson 2022-1-6
suppose you run a check between two matrix, like c=0; if A(1,1) == B (1, 1:3) c=c+1; else c=0; end and the output(ans) is (true, true, false) , I mean (1 1 0).
my counter(c) should run twice(if if A(1,1), B(1,1) and B(1,2) is equal to 8) but it will show c=0. I need C = 2
Other way I found is - Count only when it is true, like
if A(1,1) == B(1,1) c=c+1; else c=0; end
but in the second case, i have to do it for all B elements, and that's not good for big matrix. how to check and count?
  2 个评论
Andrei Bobrov
Andrei Bobrov 2017-5-24
Please attach your matrices A and B storing in mat - file.
Jan
Jan 2017-5-24
The question is not clear:
c=0;
if A(1,1) == B (1, 1:3)
c=c+1;
else
c=0;
end
Note that A(1,1) == B (1, 1:3) replies a vector, but if requires a scalar condition. Therefore Matlab inserts an all() implicitely.
and the output(ans) is (true, true, false) , I mean (1 1 0).
The shown code does not have any output. It replies either c=1 or c=0, but not [1,1,0].
my counter(c) should run twice(if if A(1,1), B(1,1) and B(1,2)
is equal to 8)
I cannot folow you here.

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回答（2 个）

Andrei Bobrov
Andrei Bobrov 2017-5-24
编辑：Andrei Bobrov 2017-5-24
c = nnz(A(:)' == B(:)); % MATLAB >= R2016b
c = nnz(bsxfun(@eq, A(:)', B(:))); % MATLAB <= R2016a
  3 个评论
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Walter Roberson
Walter Roberson 2019-12-6
Only in the sense that some objects cannot be compared. For example if A is object class tf (transfer function) and B is object class primitive chart line, then you would get an error message. But the code would be fine with A being double and B being character for example.
The original question implied that the array sizes are not the same, so the code should not be checking that they are the same.
Daniel Brower
Daniel Brower 2019-12-6
I mean if A is an nxn matrix of real numbers and B is an nxn matrix of real numbers, how would I check if A and B are similar matrices to each other, in the sense that B=S^-1*A*S.

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Jan
Jan 2017-5-24
编辑：Jan 2017-5-24
Does only A(1,1) occur in your porblem? Then:
c = (A(1,1) == B)
or if the number of equal elements is wanted
c = sum(A(1,1) == B) % or nnz() instead of sum()
If all elements of A are concerned, see either Andrei's solution, or:
c = sum(ismember(A(:), B(:)) % Or B(:), A(:) ?
  2 个评论
Zeina Abdullah
Zeina Abdullah 2022-1-5
@Jan can you help me by answer my question in my profile please . i am tring to find similar problem but I did not find
Walter Roberson
Walter Roberson 2022-1-6
https://www.mathworks.com/matlabcentral/answers/1623080-how-to-find-relationship-between-two-or-more-matrix?s_tid=srchtitle appears to be the reference

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