Dear statalist,

I have a list of companies (isin) on different dates ( variable DATE format DD/MM/YY) from 2010-2017. Some companies appear several times in the sample. If the company appear several time in a period of two year I only one to keep the first date (sooner) the company appear. I wanted to try to count by year each company (isin) but I don't know how since I need to count in a period of two years.
Here is my dataset

* Example generated by -dataex-. To install: ssc install dataex
clear
input str13 ISIN str44 ENTREPRISE str22 INFORMATION int(DATE YEAR)
"FR0000035784" "DIGIGRAM" "" 18368 2010
"FR0000062671" "TELEPERFORMANCE" "" 18444 2010
"FR0000062671" "GORGE" "" 18437 2010
"FR0000076655" "ACTIA SODIELEC" "" 18549 2010
"FR0000120271" "TOTAL" "" 18287 2010
"FR0000120578" "SANOFI" "" 18352 2010
"FR0000121501" "PSA" "" 18365 2010
"FR0000130395" "REMY COINTREAU" "" 18365 2010
"FR0010340141" "ADP" "" 18298 2010
"FR0011010198" "RISC GROUPE" "" 18302 2010
"FR0013018124" "NICOX" "" 18569 2010
"FR0013204336" "LDC" "" 18374 2010
"FR0013505062" "TECHNICOLOR" "" 18352 2010
"FR0013529815" "AVENIR TELECOM" "" 18297 2010
"FR0010340141" "ALTOM " "" 18539 2010
"FR0000036774" "DANE-ELEC MEMORY" "" 18700 2011
"FR0000044471" "RAMSAY GENERALE DE SANTE" "" 18711 2011
"FR0000073751" "BOIS ET CHIFFONS" "" 18869 2011
"FR0000075392" "ORAPI" "" 18992 2011
"FR0000120271" "TOTAL" "" 18893 2011
"FR0000121501" "PEUGEOT" "" 18772 2011
"FR0000124141" "VEOLIA" "" 18968 2011
"FR0000124414" "GASCOGNE" "" 18966 2011
"FR0000125585" "CASINO GUICHARD" "" 18941 2011
"FR0000125585" "CASINO GUICHARD" "" 18807 2011
"FR0010478248" "ATARI" "" 18736 2011
"FR0010501692" "GENERIX" "" 18892 2011
"FR0011027143" "AREVA " "" 18952 2011
"FR0011027143" "AREVA " "" 18973 2011
"FR0013018124" "NICOX" "" 18962 2011
"FR0013505062" "TECHNICOLOR" "" 18980 2011
"FR0000120537" "LAFARGE" "" 18975 2011
"FR0000121014" "LVMH" "" 18772 2011
"FR0007317813" "CS COMM" "" 18673 2011
"FR0000031122" "AIR FRANCE-KLM" "" 19165 2012
"FR0000035263" "LAFUMA DEAD - DELIST.04/12/20" "" 19154 2012
"FR0000072357" "HUIS CLOS DEAD - 15/08/14" "" 19312 2012
"FR0000073041" "PIERRE & VACANCES" "" 19284 2012
"FR0000120172" "CARREFOUR" "" 19234 2012
"FR0000120503" "BOUYGUES" "" 19177 2012
"FR0000120537" "LAFARGE DEAD - 23/10/15" "" 19025 2012
"FR0000121147" "FAURECIA" "" 19334 2012
"FR0000121147" "FAURECIA" "" 19309 2012
"FR0000121501" "PEUGEOT DEAD - CONT SEE.99278Y" "" 19186 2012
"FR0000127771" "VIVENDI" "" 19326 2012
"FR0000131732" "SPIR COMMUNICATION DEAD - DELIST.12/02/21" "" 19145 2012
"FR0000131732" "SPIR COMMUNICATION DEAD - DELIST.12/02/21" "" 19115 2012
"FR0000131906" "RENAULT" "" 19181 2012
"FR0000131906" "RENAULT" "" 19157 2012
"FR0000182479" "ARCHOS" "" 19303 2012
"FR0010259150" "IPSEN" "" 19233 2012
"FR0010340141" "ADP" "" 19351 2012
"FR0011476928" "La redoute" "" 19233 2012
"FR0000124141" "VEOLIA ENVIRON" "" 19314 2012
"FR0000130650" "dassault system" "" 19131 2012
"FR0000066540" "VM MATERIAUX" "" 19312 2012
"FR0000125486" "VINCI" "" 19086 2012
"FR0000120578" "SANOFI" "" 19179 2012
"FR0000120404 " "ACCOR" "" 19011 2012
"FR0000130007 " "ALCATEL-LUCENT DEAD - 02/11/16" "" 19284 2012
"FR0000130007 " "ALCATEL-LUCENT DEAD - 02/11/16" "" 19200 2012
"FR0013227113 " "SOITEC" "" 19311 2012
"FR0000031122" "AIR FRANCE-KLM" "" 19566 2013
"FR0000031122" "AIR FRANCE-KLM" "" 19445 2013
"FR0000044448" "NEXANS" "" 19564 2013
"FR0000120073" "L AIR LQE.SC.ANYME. POUR L ETUDE ET L EPXTN." "" 19611 2013
"FR0000120073" "L AIR LQE.SC.ANYME. POUR L ETUDE ET L EPXTN." "" 19507 2013
"FR0000120644" "DANONE" "" 19404 2013
"FR0000120859" "IMERYS" "" 19687 2013
"FR0000120859" "IMERYS" "" 19516 2013
"FR0000121261" "MICHELIN" "" 19516 2013
"FR0000124141" "VEOLIA ENVIRON" "" 19695 2013
"FR0000124141" "VEOLIA ENVIRON" "" 19437 2013
"FR0000130213" "LAGARDERE GROUPE" "" 19519 2013
"FR0000130213" "LAGARDERE GROUPE" "" 19646 2013
"FR0000130577" "PUBLICIS GROUPE" "" 19389 2013
"FR0010151589" "CAFOM" "" 19540 2013
"FR0010220475" "ALSTOM" "" 19698 2013
"FR0010313833" "ARKEMA" "" 19669 2013
"FR0010340141" "ADP" "" 19557 2013
"FR0011476928" "FNAC" "ARTICLE OK A COMPLETER" 19718 2013
"FR0000131906" "RENAULT" "OK" 19373 2013
"US3696041033" "GENERAL ELECTRIC" "" 19417 2013
"US3696041033" "GENERAL ELECTRIC" "DONNEES COMPTABLES" 19417 2013
"FR0000120271" "TOTAL" "" 19605 2013
"FR0000032682" "SNCF PARTICIPATIONS DEAD - 26/02/09" "" 19857 2014
"FR0000039620" "MERSEN (EX LCL)" "" 19752 2014
"FR0000054900" "TF1 (TV.FSE.1)" "" 19989 2014
"FR0000061129" "BOIRON" "" 19747 2014
"FR0000120503" "BOUYGUES" "" 19885 2014
"FR0000120578" "SANOFI" "" 19998 2014
"FR0000120693" "PERNOD-RICARD" "" 19933 2014
"FR0000120693" "PERNOD-RICARD" "" 19891 2014
"FR0000121261" "MICHELIN" "" 20088 2014
"FR0000121329" "THALES" "" 19743 2014
"FR0000121485" "KERING" "LIQUIDATOP?" 19732 2014
"FR0000121501" "PEUGEOT DEAD - CONT SEE.99278Y" "" 19753 2014
"FR0000121972" "SCHNEIDER ELECTRIC" "" 19851 2014
"FR0000121972" "SCHNEIDER ELECTRIC" "" 20013 2014
"FR0000124729" "GROUPE ZANNIER" "" 20054 2014

Thanks a lot of your time
Best regards