How to drop sequence of observations when the observations are zero sequently

[Aisah Aisah]

I am now cleaning my firm-level data. I have panel data which contains 19,150 observations/year for 2010-2015. I have done the following command in STATA 14.0 to indicate my panel data:

xtset firmcode, year yearly

Then I would like to drop the observation if its capital is zero during six year (2010-2015). Here is the example of my data:

Year firmcode capital

2010 24 0
2011 24 0
2012 24 0
2013 24 0
2014 24 0
2015 24 0
2010 25 0
2011 25 0
2012 25 1000
2013 25 0
2014 25 0
2015 25 0

As the firm with firmcode 24 does not have data of its capital so I will remove it, so my data will remain only firm with firmcode 25, as follows:

Year firmcode capital

2010 25 0
2011 25 0
2012 25 1000
2013 25 0
2014 25 0
2015 25 0

Would you please help how to write the command for this?

Best regards,
Aisah

[Ashish Tyagi]

Hi Aisah,

One way to do it would be to generate 2010-15 capital total and drop if it is 0. I am assuming that data timespan is strictly 2010-15 and capital cannot be negative. In that case,

by firmcode, sort: egen k_total = total(capital)
drop if k_total == 0

[Aisah Aisah]

Hi Ashish Tyagi,

Thank you very much for your help. The command worked well.

[Nick Cox]

If the smallest and largest values for each panel are both 0, then all values are 0.

bysort Year (capital) : drop if capital[1] == 0 & capital[_N] == 0

[Aisah Aisah]

Thank you very much. It is very helpful.