Have any matrix's column same number?

Hello. I have a question. If you can help me, i am pleasure.

Question: Have any matrix's column same number?

In my idea, my code just find number of diagonal.

clc;
clear;
tic
sum=0;
A=[1 2 3;4 5 3;7 8 9];
B=size(A);
m=B(1,1);
n=B(1,2);
for i=1:m
    for j=1:n
        if((A(i,j) == A(j,j) || A(j,i) == A(i,i)) && i ~= j )
            sum=sum+1;
        end
    end
end
if sum==0
    disp('different')
else
    disp('same')
end
A
toc

[James Tursa]

I don't understand the question completely. Is your current code not producing the result you want? Are you trying to find out if any diagonal elements are duplicated in the same column? Are you trying to generalize your current code? Or what? Can you give a numeric example?

[Mehmet Gurturk]

For example, you enter [3x3] matrix. My code find of same numbers to a column. If find same numbers, say 'same' but don't find, say 'different'.

[Stephen23]

@Mehmet Gurturk: the explanation is not completely clear. Can you please give us an exact example, with numbers, like this:

A = [1,2,3;4,5,6;1,8,9]

what should happen? What output do you want?

[Mehmet Gurturk]

For example,

A = [ 1 2 3; 
      4 5 6; 
      7 8 9]  output = Different

        A = [ 1 2 3;
              4 5 6; 
              1 8 9]  output = Same

But

       A = [ 1 2 *3* ;
             4 5 *3* ; 
             7 8  9]  output = *Different*

I want to do

     A = [ 1 2 *3* ;
           4 5 *3* ;
           7 8  9]  output = *Same*

[Mehmet Gurturk]

My code just find to numbers of diagonal matrix

[Joseph Cheng]

Stephen he is trying to say that in the code he has presented it marks the second example as "different" due to the fact that his code only checks the diagonals.

[Stephen23]

@Joseph Cheng: thank you for the clarification, I was a little bit confused about the meaning.

Answer 1

[Joseph Cheng]

you can use the function unique() to determine if there are repeated values within the matrix

x = randi(10,4,4);
disp(x);
for ind = 1:size(x,2)
   if numel(unique(x(:,ind)))<numel(x(:,ind))
       disp('same')
   else
       disp('different')
   end    
end

[Joseph Cheng]

if you only want 1 answer then

x = randi(10,4,4);
disp(x);
same = 0;
for ind = 1:size(x,2)
   if numel(unique(x(:,ind)))<numel(x(:,ind))
       same = same+1;
   end    
end
if same>0
    disp('same');
else
    disp('different');
end

Answer 2

[Stephen23]

Here is a very fast and simple solution that does not require any loops (i.e. fully vectorized code). An output of 0 indicates different, and output of 1 indicates same.

>> A = [1,2,3; 4,5,6; 7,8,9]
A =
     1     2     3
     4     5     6
     7     8     9
>> any(any(0==diff(sort(A))))
ans =
     0
>> A = [1,2,3; 4,5,6; 1,8,9]
A =
     1     2     3
     4     5     6
     1     8     9
>> any(any(0==diff(sort(A))))
ans =
     1

Here it is on your second example matrix:

>> A = [1,2,3; 4,5,3; 7,8,9]
A =
     1     2     3
     4     5     3
     7     8     9
>> any(any(0==diff(sort(A))))
ans =
     1

And if you want to know which column contains repeated values then simply remove one of the any commands:

>> any(0==diff(sort(A)))
ans =
     0     0     1

This code works very simply: it sorts the columns, then uses diff to find if any adjacent values are the same. You can use the all(..) to control the if statement, like this:

if all(...)
    disp('same')
else
    disp('different')
end

[Joseph Cheng]

very nice.. I like the use of sort.

Answer 3

[Mehmet Gurturk]

Thank you so much :)