How to identify all the cases in a list of binary variables

[Man Yang]

Hello folks, I have a list of binary variables and I want to generate a new variable describing the combination. Below is part of what my data looks like

id    sch_grade_ps    sch_grade_kg    sch_grade_g01    sch_grade_g02    sch_grade_g03    sch_grade_g04    sch_grade_g05    sch_grade_g06    sch_grade_g07
1    0    0    0    0    0    0    0    1    1
2    0    0    0    0    0    0    0    1    1
3    0    0    0    0    0    0    0    1    1
4    0    0    0    0    0    0    1    1    1
5    0    0    0    0    0    0    0    0    1
6    0    0    0    0    0    0    0    0    0
7    0    0    0    0    0    0    1    1    0
8    0    0    0    0    1    1    0    0    0
9    1    1    0    0    0    0    0    0    0
10    1    0    1    1    0    0    0    0    0
11    0    0    0    0    0    0    1    1    1
12    0    0    0    0    0    0    0    1    1
13    1    1    1    1    1    1    0    0    0
14    1    0    0    0    1    1    1    0    0
15    0    0    0    0    0    0    0    0    0
16    1    0    0    0    1    1    1    0    0
17    0    0    0    0    0    0    0    0    0
18    1    1    1    1    0    0    0    0    0
19    1    1    1    1    0    0    0    0    0
20    0    0    0    0    0    0    0    1    1
21    0    0    0    0    0    0    0    0    0
22    1    1    1    1    1    1    0    0    0
23    0    0    0    0    0    0    0    1    1
24    1    1    1    1    1    1    1    0    0

I want to create a new variable, say grade_level and it describes the grades covered by each ID. For instance, for ID=1, the new variable will has value such as "6-7" or "6&7", etc. Anyway, my goal is to get a shorter version of the grade levels for each ID. The next step is to group IDs that have the same grade levels together. I did some search and found a command called Tuples but I feel this is not exactly what I want. Any ideas? Thanks!

[Clyde Schechter]

One way to do this is:

egen grade_level = concat(sch_grade_ps sch_grade_kg sch_grade_g01 ///
sch_grade_g02 sch_grade_g03 sch_grade_g04 sch_grade_g05 ///
sch_grade_g06 sch_grade_g07), punct("&")