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