Hey guys,

I am currently trying to figure out how to find unobserved values. I have different sic codes (labeled "sic), accordingly values for sale (labeled "sale") and I want to look at a time period of 26 years, namely from 1984 to 2010.
I want to know, whether each of the sic codes has data of sale within the 26 years. I know, in fact, that this is not the case for each sic code.
Do you know how I can find out which of the sic codes does not have sale data of all year (e.g. lags year 1989 and 2008 and thus has only 24 values)?

THANK YOU SO MUCH IN ADVANCE!!!