Identifying observations with consecutive 3 quarters.

[River Huang]

Dear All, Suppose the data set is:

* Example generated by -dataex-. For more info, type help dataex
clear
input long com float yq double id
1 173 505823929
1 175 505823929
1 177 505823929
1 238 506119843
1 239 506119843
1 240 506119843
1 241 506119843
1 242 506119843
1 243 506119843
1 244 506119843
1 245 506119843
1 246 506119843
2 217     50472
2 218     50472
2 219     50472
2 220     50472
2 221     50472
2 222     50472
2 223     50472
2 224     50472
2 225     50472
2 226     50472
2 227     50472
2 228     50472
2 229     50472
2 230     50472
2 231     50472
2 232     50472
2 233     50472
2 234     50472
2 235 504171416
2 235     50472
2 236     50472
2 236 504171416
2 237 504171416
2 237     50472
2 238     50472
2 239     50472
2 240     50472
2 241     50472
2 242     50472
2 243     50472
2 244     50472
2 245 506119843
2 245     50472
2 246     50472
4 222 504895009
4 223 504895009
4 224 504895009
4 225 504895009
4 226 504895009
4 227 504895009
4 228 504895009
4 229 504895009
4 230 504895009
4 231 504895009
4 232 504895009
6 173   5019084
6 175   5019084
6 177   5019084
6 179   5019084
6 181   5019084
6 183   5019084
6 185 505824461
6 187 505824461
6 189 505824461
6 190 505824461
6 191 505824461
6 192 505824461
6 193 505824461
6 194 505824461
6 195 505824461
6 196 505824461
6 197 505824461
6 198 505824461
6 199 505824461
6 200 505824461
6 201 505824461
6 202 505824461
6 203 505824461
6 204 505824461
6 205 505824461
6 206 505824461
6 207 505824461
6 208 505824461
6 209 505824461
6 210 505824461
6 211 505824461
6 212 505824461
6 213 505824461
6 214   5021897
6 214 505824461
6 215   5021897
6 215 505824461
6 216   5021897
6 216 505824461
6 217   5021897
6 217 505824461
6 218   5021897
6 218 505824461
end
format %tq yq

The purpose is, for each shareholder (`id') in each firm (`com'), to construct a dummy, which is 1if the shareholder appears in consecutive 3 quarters (inclduing the current, previous 1 & 2 quarters), 0 otherwise.
Any suggestions are highly appreciated.

[Øyvind Snilsberg]

by com id (yq), sort: gen wanted = (2*yq - yq[_n-1] - yq[_n-2]) == 3

[River Huang]

Dear Øyvind, Many thankd for this helpful solution.