Find rows in matrix based on columns value

Asked by Stewart Tan on 2 Sep 2019

Latest activity Commented on by Andrei Bobrov on 2 Sep 2019

3 views (last 30 days)

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.

1 Comment

Andrei Bobrov on 2 Sep 2019

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

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3 Answers

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Answer by Robert U on 2 Sep 2019

Edited by Robert U on 2 Sep 2019

Accepted Answer

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

2 Comments

madhan ravi on 2 Sep 2019

? 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 on 2 Sep 2019

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

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Answer by madhan ravi on 2 Sep 2019

Edited by madhan ravi on 2 Sep 2019

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

edit:

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

3 Comments

Andrei Bobrov on 2 Sep 2019

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 on 2 Sep 2019

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 on 2 Sep 2019

All right! +1.

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Answer by Andrei Bobrov on 2 Sep 2019

Edited by Andrei Bobrov on 2 Sep 2019

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')));

[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);

6 Comments

Show 3 older comments

Robert U on 2 Sep 2019

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 on 2 Sep 2019

I'm sorry Robert, my mistake!

Stewart Tan on 2 Sep 2019

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!

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