Find rows in matrix based on columns value

Asked by Stewart Tan

Stewart Tan (view profile)

on 2 Sep 2019
Latest activity Commented on by Andrei Bobrov

Andrei Bobrov (view profile)

on 2 Sep 2019
Accepted Answer by Robert U

Robert U (view profile)

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

Andrei Bobrov (view profile)

on 2 Sep 2019
find(mat(:,2) == 10 & mat(:,3) == 11)

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Answer by Robert U

Robert U (view profile)

on 2 Sep 2019
Edited by Robert U

Robert U (view profile)

on 2 Sep 2019

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 (view profile)

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

Robert U (view profile)

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.

madhan ravi (view profile)

on 2 Sep 2019
Edited by madhan ravi

madhan ravi (view profile)

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

Andrei Bobrov (view profile)

on 2 Sep 2019
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 (view profile)

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

Andrei Bobrov (view profile)

on 2 Sep 2019
All right! +1.

Answer by Andrei Bobrov

Andrei Bobrov (view profile)

on 2 Sep 2019
Edited by Andrei Bobrov

Andrei Bobrov (view profile)

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

Robert U (view profile)

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

Andrei Bobrov (view profile)

on 2 Sep 2019
I'm sorry Robert, my mistake!
Stewart Tan

Stewart Tan (view profile)

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!