Changing a nominal variable (like firm ID) into a dummy variable?

[Alp Marta]

Hi,
I need some help to create a dummy variable from a nominal variable. I want to make a dummy for my person IDs as mover or stayer. If the person stays in the same firm, then the person is a stayer (value 0) and if s/he chnages the firm, s/he is a mover (with value 1). I would appreciate to know the command or a relevant reference to read aboout it.

Person ID	Firm ID	Year	stayer/mover
1	100	2015	0
1	100	2016	0
1	115	2017	1
1	116	2018	1
2	113	2015	0
2	118	2016	1
2	118	2017	0
2	140	2018	1

[Leonardo Guizzetti]

If I have understood your question correctly, you only care about whether the person changes firms in their entire history, then this will suffice. The logic is straightforward: for each observation, return a zero if the person stays at the same firm as their first recorded year, or else they moved and a 1 is returned. The max value over all years for the person then records if they ever moved, or not.

input byte(pid) int(firmid year)
1 100 2015
1 100 2016
1 115 2017
1 116 2018
2 113 2015
2 118 2016
2 118 2017
2 140 2018
end

bys pid (year) : egen byte mover = max(cond(firmid != firmid[1], 1, 0))
list

Result

. list

     +-----------------------------+
     | pid   firmid   year   mover |
     |-----------------------------|
  1. |   1      100   2015       1 |
  2. |   1      100   2016       1 |
  3. |   1      115   2017       1 |
  4. |   1      116   2018       1 |
  5. |   2      113   2015       1 |
     |-----------------------------|
  6. |   2      118   2016       1 |
  7. |   2      118   2017       1 |
  8. |   2      140   2018       1 |
     +-----------------------------+

[Alp Marta]

Thank you Leonardo for the quick feedback. I just want to compare the firm change with previous year not necessay the firs recorded year. For example, person 2 in 2018 changed his firm from 118 to 140, so he is in this year a mover and gets the value 1.

[Leonardo Guizzetti]

In that case you need the following.

bys pid (year) : gen byte mover = cond(_n>1 & firmid != firmid[_n-1], 1, 0)

[Alp Marta]

perfect and many thanks