drop individuals by the condition

[OBADA ALMAJALI]

hello everyone,

could anyone help me to find an appropriate command for the following condition:

I have dummy variables zero and one, I want to drop firms that have not dummy variable one in all year.

for example, I have the following dataset

id year dummy
1 2000 1
1 2001 1
1 2002 0
1 2003 0
1 2004 0
1 2005 1
2 2000 0
2 2001 0
2 2002 0
2 2003 0
2 2004 0
3 20050

So I want to keep id 1 because there is dummy variable one in some years and I want to drop id 2 because all years have dummy zero and so on.

Could anyone help me to find the command?

[Nick Cox]

Question is inconsistent: is the criterion 1 in all years or 1 in some years?

For all years

bysort id (dummy) : drop if dummy[1] == 0

For some years

bysort id (dummy) : keep if dummy[_N] == 1

[OBADA ALMAJALI]

Dear Nick Cox

Thank you very much