Dataset with multiple identifiers

[Marco Errico]

Dear all

I have an apparently simple question which I struggle in the way to approach it

I have two identifiers, namely gvkey (company) and isin (stock) on a quarter panel.

Generally each gvkey correspond to one isin. In other words, one company (identifiyed by gvkey) in most of the cases can have only one stock traded on exchange(isin). Nevertheless there might be cases where one company has two stocks traded.

I want to identify these companies by creating an indicator. How can I approach to it?

* Example generated by -dataex-. To install: ssc install dataex
clear
input str6 gvkey str12 isin float calendar_qtr
"284856" "AEDFXA0M6V00" 208
"284856" "AEDFXA0M6V00" 209
"284856" "AEDFXA0M6V00" 210
"284856" "AEDFXA0M6V00" 211
"284856" "AEDFXA0M6V00" 212
"284856" "AEDFXA0M6V00" 213
"284856" "AEDFXA0M6V00" 214
"284856" "AEDFXA0M6V00" 215
"284856" "AEDFXA0M6V00" 216
"284856" "AEDFXA0M6V00" 217
"284856" "AEDFXA0M6V00" 218
"284856" "AEDFXA0M6V00" 219
"284856" "AEDFXA0M6V00" 220
"284856" "AEDFXA0M6V00" 221
"284856" "AEDFXA0M6V00" 222
"284856" "AEDFXA0M6V00" 223
"284856" "AEDFXA0M6V00" 224
"284856" "AEDFXA0M6V00" 225
"284856" "AEDFXA0M6V00" 226
"284856" "AEDFXA0M6V00" 227
"284856" "AEDFXA0M6V00" 228
"284856" "AEDFXA0M6V00" 229
"284856" "AEDFXA0M6V00" 230
"284856" "AEDFXA0M6V00" 231
"284856" "AEDFXA0M6V00" 232
"284856" "AEDFXA0M6V00" 233
"284856" "AEDFXA0M6V00" 234
"284856" "AEDFXA0M6V00" 235
"284856" "AEDFXA0M6V00" 236
"284856" "AEDFXA0M6V00" 237
"284856" "AEDFXA0M6V00" 238
"284856" "AEDFXA0M6V00" 239
"284856" "AEDFXA0M6V00" 240
"284856" "AEDFXA0M6V00" 241
"284856" "AEDFXA0M6V00" 242
"284856" "AEDFXA0M6V00" 243
"284856" "AEDFXA0M6V00" 244
"284856" "AEDFXA0M6V00" 245
"284856" "AEDFXA0M6V00" 246
"284856" "AEDFXA0M6V00" 247
"324216" "AEDFXA1EN018" 219
"324216" "AEDFXA1EN018" 223
"324216" "AEDFXA1EN018" 224
"324216" "AEDFXA1EN018" 225
"324216" "AEDFXA1EN018" 226
"324216" "AEDFXA1EN018" 227
"324216" "AEDFXA1EN018" 228
"324216" "AEDFXA1EN018" 229
"324216" "AEDFXA1EN018" 230
"324216" "AEDFXA1EN018" 231
"324216" "AEDFXA1EN018" 232
"324216" "AEDFXA1EN018" 233
"324216" "AEDFXA1EN018" 234
"324216" "AEDFXA1EN018" 235
"324216" "AEDFXA1EN018" 236
"324216" "AEDFXA1EN018" 237
"324216" "AEDFXA1EN018" 238
"324216" "AEDFXA1EN018" 239
"324216" "AEDFXA1EN018" 240
"324216" "AEDFXA1EN018" 241
"324216" "AEDFXA1EN018" 242
"324216" "AEDFXA1EN018" 243
"324216" "AEDFXA1EN018" 244
"324216" "AEDFXA1EN018" 245
"324216" "AEDFXA1EN018" 246
"324216" "AEDFXA1EN018" 247
""       "AGP8696W1045" 232
""       "AGP8696W1045" 233
""       "AGP8696W1045" 234
""       "AGP8696W1045" 235
""       "AGP8696W1045" 236
""       "AGP8696W1045" 237
""       "AGP8696W1045" 238
""       "AGP8696W1045" 239
""       "AGP8696W1045" 240
""       "AGP8696W1045" 241
""       "AGP8696W1045" 242
""       "AGP8696W1045" 243
""       "AGP8696W1045" 244
""       "AGP8696W1045" 245
""       "AGP8696W1045" 246
""       "AGP8696W1045" 247
""       "AN8068571086" 232
""       "AN8068571086" 233
""       "AN8068571086" 234
""       "AN8068571086" 235
""       "AN8068571086" 236
""       "AN8068571086" 237
""       "AN8068571086" 238
""       "AN8068571086" 239
""       "AN8068571086" 240
""       "AN8068571086" 241
""       "AN8068571086" 242
""       "AN8068571086" 243
""       "AN8068571086" 244
""       "AN8068571086" 245
""       "AN8068571086" 246
""       "AN8068571086" 247
"101618" "ANN4327C1220" 208
"101618" "ANN4327C1220" 209
end
format %tq calendar_qtr

[Roman Mostazir]

egen morethanone = tag(gvkey isin)

[Andrew Musau]

For two or more, count the tagged observations from Roman's code and create the indicator if greater than 1 or

bys gvkey (isin): gen count= sum(isin[_n-1]!=isin)
bys gvkey: egen wanted=max(count>1)

[Marco Errico]

Dear Roman Mostazir and Andrew Musau

Thank you so much for your clarifications.

Andrew, thanks, Thanks to your insight I was able to identify different groups (if a company has 2 -3 etc.. stocks)