Loop backwards and select subset of rows that meet criteria

I am trying to loop backwards to select rows that meet a certain criteria. The criteria is "t" which is a date. From there I need to loop backwards through the first column (which is a single datenum) for as long as the difference between the datenums is =1. Once the difference is no longer 1, the loop can stop and all rows in which the datenum had a difference of 1 can be saved. Here is an example: If t = 712896 and

A=
  712572  1950  12  15  -0.68
  712573  1950  12  16  -1.84
  712574  1950  12  17  -1.81
  712575  1950  12  18  -1.51
  712576  1950  12  19  -1.49
  712893  1951  11  1  -1.38
  712894  1951  11  2  -2.56
  712895  1951  11  3  -2.68
  712896  1951  11  4  -2.90
  712897  1951  11  5  -2.27
  712898  1951  11  6  -1.83
  712899  1951  11  7  -1.57
  712900  1951  11  8  -1.80

 So the output would be:     
    712893  1951  11  1  -1.38
    712894  1951  11  2  -2.56
    712895  1951  11  3  -2.68

Here is the loop I have so far:

           for k=length(A):-1:1;
                if A(k,1) == t;

                      (part I'm having trouble with)

                end
            end

Answer 1

[Gareth Lee]

if you want to use loop, it is showed below:

tindex = find(A(:,1)==t);
for j = tindex:-1:2
    if(A(j,1)-A(j-1,1)==1)
        B(j-1,:)= A(j-1,:);
    else
        break;
    end
end
reshape(nonzeros(B),'',nnz(any(B)))

[Tyler Smith]

When I don't use a loop I get the error "Subscript indices must either be real positive integers or logicals." But the loop version works great! Thanks.

Answer 2

[Gareth Lee]

you can solve it without loop, e.g

 B = find(diff(A(1:find(A(:,1)==t),1))~=1);
 result = A(B(end)+1:find(A(:,1)==t)-1,:);