Data separation

[Caroleen Gomez]

Hello,
I have US firms data from compustat and exeucomp. I have do my analysis for which I want to use only firms that were part of S&P 500 index. As there are firms present which are part of different index. Could you please tell how to perform the coding to eliminate rest of the data and keeping on firms with S&P 500 index.

Thanks in advance

[Rich Goldstein]

if you have a listing of the firms in the S&P, just make sure that both files are sorted in the same way and do a merge (whether it is 1:1 or 1:m or m:1 depends on whether the other data set is the master or using and whether it has more than one observation/firm); see "h merge"

[Caroleen Gomez]

Does this merging affect dataset? As I have merged and append using four dataset. Also the file contains those firms as well which are not from s&p 500 index. And I want do my analysis using s&p500 firms.