Identifying missing values between identical value!

[Mehdi Amani]

Hi everyone,
I have faced a problem, and it takes so much time for me and couldn't figure it out.
I have a large dataset of people and the firm they were working over years. Since the data is sampled, some individuals have missing information about firms. I would like to replace firms in the years that the data is missing and, with a dummy variable, mark it for future usage.
To clarify more, In a simple case, I would like to identify the ones with the red mark.
If it would be helpful let me share my unsuccessful attempts
Thanks in advance.

[Carlo Lazzaro]

Mehdi:
I do hope that what follows can be helpful:

. set obs 6
Number of observations (_N) was 0, now 6.

. g wanted=1 in 1/3

. replace wanted=2 in 5/6

. bysort wanted: gen check_missing=1 if wanted==.

. replace check_missing=0 if wanted!=.


. list

     +-------------------+
     | wanted   check_~g |
     |-------------------|
  1. |      1          0 |
  2. |      1          0 |
  3. |      1          0 |
  4. |      2          0 |
  5. |      2          0 |
     |-------------------|
  6. |      .          1 |
     +-------------------+

.

[Nick Cox]

Please note from https://www.statalist.org/forums/help#stata that images of data are not as helpful as you hope. Please use dataex to provide data examples.

This works for your example.

* Example generated by -dataex-. For more info, type help dataex
clear
input float group
5
5
5
.
5
5
.
.
8
.
.
8
end

gen long obsno = _n 

ipolate group obsno, gen(group_i)

gen wanted = missing(group) & group_i == group_i[_n-1]

list, sepby(wanted)

     +----------------------------------+
     | group   obsno   group_i   wanted |
     |----------------------------------|
  1. |     5       1         5        0 |
  2. |     5       2         5        0 |
  3. |     5       3         5        0 |
     |----------------------------------|
  4. |     .       4         5        1 |
     |----------------------------------|
  5. |     5       5         5        0 |
  6. |     5       6         5        0 |
  7. |     .       7         6        0 |
  8. |     .       8         7        0 |
  9. |     8       9         8        0 |
     |----------------------------------|
 10. |     .      10         8        1 |
 11. |     .      11         8        1 |
     |----------------------------------|
 12. |     8      12         8        0 |
     +----------------------------------+

The idea is that interpolation within say 5 . 5 or 8 . . 8 will copy the constant on either side, but that won't work otherwise.

In your full problem ipolate should be specified with a by() option.

[Mehdi Amani]

Thanks for quick reply.
I think I couldn't explain my problem. I would like to just mark the missing one between two same-number values and not others.

[Nick Cox]

Please see now revised #3.