I have a matrix and I am actually interested in obtaining a vector that will consist of the first column in each row that has values lower certain value.

I have a matrix and I am actually interested in obtaining a vector that will consist of the first column in each row that has values lower 3. e.g if I have A=[ 5 7 8 3 2 ;6 2 1 4 4;1 2 3 4 5; 4 5 2 1 3]. I expect an Ans: [5;2;1;4]

Answer 1

[Saint]

Thanks Star Strider and MathsReallyWork. I kind of figure it out.Ans: [5;2;1;3]

dmax=3
Nrows=4
 A=[5 7 8 3 2 ;6 2 1 4 4;1 2 3 4 5; 4 5 2 1 3]
for i=1:Nrows
  B=A(i,:)';
  a(i)=find(B<dmax,1,'first') ;
end
b=a'

[Stephen23]

It is simpler and more efficient to process the whole array at once, rather than using a loop:

>> C = A.';
>> idx = C<dmax;
>> [col,row] = find(idx & cumsum(idx,1)==1)
col =
     5
     2
     1
     3
row =
     1
     2
     3
     4

Answer 2

[MathReallyWorks]

Hello saint,

Your question is not clear. Please edit it.

By the description of your question I can guess that you want first column of each row provided that entry is less than 3. In that case this code works well:

 A = [ 5 7 8 3 2 ;6 2 1 4 4;1 2 3 4 5; 4 5 2 1 3];
newA = A(A(:,1)<3,1)

But, then you said you are expecting [5;2;1;4] which is contradictory to your question.

[5;6;1;4] is possible as it contains all first element.