logical arry indexing: how to extract columns that match a criterion

I want to extract columns from a 2D array, when the element in row 3 of the column matches a criterion. Example:

>> rng(42); a=rand(3,5); disp(a)
    0.3745    0.5987    0.0581    0.7081    0.8324
    0.9507    0.1560    0.8662    0.0206    0.2123
    0.7320    0.1560    0.6011    0.9699    0.1818

I want to pick out the columns of a for which the row 3 element is between 0.6 and 0.8. In this example, that means I want an array with columns 1 and 3 of a, since those columns meet the row 3 criterion. The following for loop does the job, but it seems inelegant.

>> j2=1;
for j1=1:5
    if a(3,j1)>.6 && a(3,j1)<.8
        b(:,j2)=a(:,j1); 
        j2=j2+1; 
    end 
end 
disp(b)
    0.3745    0.0581
    0.9507    0.8662
    0.7320    0.6011

Here are some failed attempts to do it with logical indexing.

>> b=a(a(4,:)>.6 && a(4,:)<.8); disp(b)
Index in position 1 exceeds array bounds (must not exceed 3).
>> b=a(a(4,:)>.6 && a(4,:)<.8,:); disp(b)
Index in position 1 exceeds array bounds (must not exceed 3).
>> b=(a(4,:)>.6 && a(4,:)<.8,:); disp(b)
Error: Invalid expression. 
>> tf=a>.6 & a<.8; 
>> b=a(tf(4,:)); disp(b)
Index in position 1 exceeds array bounds (must not exceed 3).

Thank you for your assistance.

Answer 1

[David Hill]

b=a(3,:);%whatever row
c=a(:,b>=.6&b<=.8);

[William Rose]

Thank you David.

The right answer always looks obvious in retrospect.

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