What can I do for this Matrix manipulation

I have two types of matrix (29*1 and 168*1). K: 29*1, R: 168*1

The values of K represent specific n-th row of R. And I'd like to take values of R corresponding to K values. In the end, I should have this matrix, R'(29*1) from R(168*1).

What can I do for that?

[Rik]

It is not entirely clear to me what you mean. This is my best guess:

rate(k)

Also, I would change your code a bit in a few places:

number=unique(B(:,1));
tn=numel(number);
initial=rand(1,3);
rate=zeros(tn,1);R2_value=zeros(tn,1);
ft = fittype('a*exp(-x/b)+c');
for i=1:tn
    current=ismember(B(:,1),number(i));
    [F,gof2] = fit(B(current,2),B(current,3),ft,'StartPoint',initial);
    rate(i) = 1/F.b;
    R2_value(i)=gof2.rsquare;
end
k=find(R2_value>0.7)

[Jaehwi Bong]

Thank you for your advice, your way is more efficient.

I'm sorry I've changed my question while you commented.

Can I take the value of R corresponding to K (n-th row of R)?

[Rik]

Is this what you mean?

R2_value(k)

You're making it confusing by not explaining what you mean with a small example.

[Jaehwi Bong]

Thank you! I got it :)