Panel data - count groups

[Ronald Biefinger]

Hello,
probably there is a very simple solution to my problem. I am still stuck...
I have panel data and want to count all the groups that satisfy a certain condition, i.e. a dummy variable ==1. All my groups have a varying number of observations (some have only 3, some have 6, and so on). The dummy variable is time-invariant / does not change over time and remains the same value per group. I would like to know how many individual groups have dummy var == 1 and how many var == 0. Please help me out here, thank you!

[Clyde Schechter]

Well, since you say that the dummy variable is time-invariant, it's particularly simple:

egen flag = tag(group)
tab dummy_var if flag

[Ronald Biefinger]

Great, thank you very much!

[Ronald Biefinger]

I have a question similar to my initial post.

The code Clyde Schechter provided was just working fine. Now I have the problem that I want to count all groups if a (dummy) variable of each group's second observation is equal to 1. How can I accomplish that?

Thank you!

[Nick Cox]

 
bysort panelid (time): gen wanted = myvar[2] == 1 
su if wanted

For a balanced panel, this could be easier: e.g.

count if myvar & year == 1982

for a panel dataset with years 1981...whatever.