Dear all,

I have a very big data set with a survival structure that I want to compress/collapse. Right now the data look like this:
ID t0 t1 y x1 x2
1 0 1 0 0 0
1 1 2 0 0 0
1 2 3 0 3 1
1 3 4 0 2 1
1 4 5 0 2 1
1 5 6 1 2 0
1 6 7 0 1 0
1 7 8 0 2 1
1 8 9 1 2 1
t0 and t1 specify the start and end time, y is some outcome and x1 and x2 are time-varying variables.
What I want to do is to collapse spells of t0 t1 where none of the time-varying variables (including y) vary for a period.

In other words, I want to transform the data above to look like this:
ID t0 t1 y x1 x2
1 0 2 0 0 0
1 2 3 0 3 1
1 3 5 0 2 1
1 5 6 1 2 0
1 6 7 0 1 0
1 7 8 0 2 1
1 8 9 1 2 1

Example code:
Code:
input str1 id     t0         t1         y         x1         x2
        1        0        1        0        0        0    
        1        1        2        0        0        0
        1        2        3        0        3        1
        1        3        4        0        2        1
        1        4        5        0        2        1
        1        5        6        1        2        0
        1        6        7        0        1        0
        1        7        8        0        2        1
        1        8        9        1        2        1
end