Find rows in matrix based on columns value

If i have a matrix:

mat = [1 2 3 4; 
       5 6 7 8; 
       9 10 11 12];

How do i find the row index where the column has value 10 and 11 for example? In this case, the row index will be 3 since it has columns with 10 and 11.

I tried doing something like:

   find(mat(:,2) == 10 && mat(:,3) == 11)

But it doesn't work.

[Andrei Bobrov]

find(mat(:,2) == 10 & mat(:,3) == 11)

Answer 1

[Robert U]

Hi Steward Tan,

in the given matrix there is no single column that contains the values 10 AND 11. If you want to find the rows that contain 10 AND 11 you could use:

tmp = arrayfun(@(dIn) find(any(mat(dIn,:) == 10) & any(mat(dIn,:) == 11)),1:size(mat,1),'UniformOutput',false);
tmp(cellfun(@isempty,tmp)) = {0};
row = find(cell2mat(tmp));

If you want to find the values 10 OR 11 within the matrix, and return the rows they have been found in, one way might be:

mat = [1 2 3 4; 
       5 6 7 8; 
       9 10 11 12];
   
[row,~] = find(mat == 10 | mat == 11);
row = unique(row);

Kind regards,

Robert

[madhan ravi]

? There are only three rows whereas this answer gives 6 & 9 ?

>> mat = [1 2 3 4; 
       5 6 7 8; 
       9 10 11 12];
   
[row,~] = unique(find(mat == 10 | mat == 11))

row =

     6
     9

>> 

[Robert U]

My bad, the unique command needs to be written in an extra line to capture rows from find. I edited my answer.

Answer 2

[madhan ravi]

ix = sum(ismember(mat,[10,11]),2)==2;
row_index = find(ix)

edit:

row_index = find(sum(~mod(mod(mat,10),11),2)==1)

[Andrei Bobrov]

Hi Madhan!

Your result for follow case:

mat = [10	2	3	8
5	7	10	3
9	10	11	11];

>> row_index = find(sum(~mod(mod(mat,10),11),2)==1)
row_index =
     1
     2
     3
>> 

[madhan ravi]

Yes Andrei, I realised just before your comment :). Hi Andrei, how about:

m=any(~mod(mat,10),2) & any(~mod(mat,11),2);
w=find(m)

[Andrei Bobrov]

All right! +1.

Answer 3

[Andrei Bobrov]

My case for mat:

mat = [1    11     3    10
     5     6    10    10
     9    10    11    12];
 
mat2 = sort(mat,2);
[m,n] = size(mat);
mat3 = mat2([(1:end-m)',(m+1:end)']);
iii = mod((1:m*n-m)'-1,m)+1;
out = sort(iii(ismember(mat3,[10,11],'rows')));

or

[i1,~] = find(mat == 10);
[i2,~] = find(mat == 11);
out = intersect(i1,i2);

another variant:

out = all(any(mat == reshape([10,11],1,1,[]),2),3);

[Andrei Bobrov]

for my case:

mat = [1    11     3    10
     5     6    10    10
     9    10    11    12];

Madhan's result:

>> ix = sum(ismember(mat,[10,11]),2)==2;
row_index = find(ix)
row_index =
     1
     2
     3
>> 

[madhan ravi]

Ah thanks Andrei, +1

[Robert U]

The description of the cited solution says "If you want to find the values 10 OR 11 within the matrix, and return the rows they have been found in, [...]". That is what it does.

[Robert U]

What Steward Tan might want is to find rows containing 10 AND 11 within the matrix, but he did not describe it as that.

row = find(arrayfun(@(ind) any(mat(ind,:) == 10) & any(mat(ind,:) == 11),1:size(mat,1)));

Kind regards,

Robert

[Andrei Bobrov]

I'm sorry Robert, my mistake!

[Stewart Tan]

Thank you all for the various answers for this question of mine. Wish there was a way to accept more than one answers as they had been of good help. Voted up! Cheers!