Asked by Stewart Tan
on 2 Sep 2019

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.

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

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

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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)

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')));

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);

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

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