How extract specific data from a large matrix and save in new matrix?

Hi, I have a matrix say"mv" ( 45x1) and another matrix called "a" (a=15252x23). Every value of 'mv' is present in 'a' (first column of a), so i want a new matrix say "b" where the data of only mv id should be there and rest should be omitted. I am writing code but unable to get desired answer. Below is the code. Please help.

for i = 1:length (mv);
    if a (:,1) == mv;
        mv_ramp (i,:) = a(a(:,1)== mv(i),:); % mv_ramp is new matrix where extracted data should be stored
    end;
end;

Output: Matrix dimensions must agree (Error is coming). And Only one vehicle id data is stored in mv_ramp. Please identify my mistake. Thanks

[the cyclist]

Is each value of in mv guaranteed to be in a(:,1) exactly once, or could it be duplicated? If the latter, then you are trying to copy several rows into one.

Also, are you sure that each values of mv is exactly equal to the values in a(:,1), or could they possibly be different by tiny, floating-point error?

[Yasir Ali]

Actually, mv is obtained using "unique" command and there are multiple value of mv in 'a'. Yes i am trying to copy all rows of same id from mv but getting issue. I think this might help you to understand my problem. Thanks

Answer 1

[Andrei Bobrov]

mv_ramp = a(ismember(a(:,1),mv),:);

Answer 2

[the cyclist]

If you are guaranteed that the value of mv is in a(:,1), then you actually do not need the if statement.

This simple version worked for me:

mv = [3 2 1]';

a = [2 16;
     1 17;
     3 18];

for i = 1:length(mv)
    mv_ramp (i,:) = a(a(:,1)== mv(i),:);
end

This could also have been vectorized as follows:

[~,loc] = ismember(mv,a(:,1));
mv_ramp = a(loc,:)

[Yasir Ali]

Thank you for your response. I just ran your first given code. It is giving this issue (Subscripted assignment dimension mismatch). The values of mv are in single column of matrix.

for i = 1:length (mv);
  mv_ramp (i,:) = a(a(:,1)== mv(i),:);
end;

Your second code did work, but it is taking only one value of mv from 'a', like there are multiple values of mv in 'a' so how to include all values? Thank you for you rhelp.

[Andrei Bobrov]

+1

[the cyclist]

Oops! I accidentally swapped the argument order in ismember. Andrei got it right.