Hello, I am using a person-firm-level panel data for analysis of wage differentials. But I found that in my dataset has some duplicated identifiers for different firms, e.g: the same identity numbers for two firms in two different regions in the same year. I want to:
1) Identify this firms ids
2) Drop these firms ids

input double cnpjcei long município float ano
459400009379 110001 2010
500088456682 110002 2018
500072511785 110002 2015
500072511785 110002 2018
512209712772 110002 2013
260040022389 110002 2010
500072511785 110002 2017
260040022389 110002 2010
260040022389 110002 2013
260040022389 110002 2013