当两组一个接一个地重复时，我怎样才能找到每组中R组中的第一次和最后一次观察

data is below

数据如下

dialled     Ringing     state   duration
NA  NA  NA  0
NA  NA  NA  0
NA  NA  NA  0
NA  NA  NA  0
123 NA  NA  0
123 NA  NA  0
123 NA  NA  0
123 NA  NA  60
NA  NA  active  0
NA  NA  active  0
NA  NA  inactive    0
NA  NA  inactive    0
123 NA  inactive    0
123 NA  inactive    0
123 NA  inactive    0
NA  NA  inactive  0
NA  NA  inactive  0
NA  NA  inactive    0
222 NA  inactive    0
222 NA  inactive    0
222 NA  inactive    37
NA  NA  active  0
NA  NA  active  0
NA  NA  inactive    0
123 NA  inactive    0
123 NA  inactive    0
123 NA  active  60
NA  NA  active  0
NA  NA  active  0
NA  NA  active  0
NA  NA  active  0
123 NA  inactive    0
123 NA  inactive    0
123 NA  inactive    0


answer i am looking for is

dialled     Ringing     state   duration
123 NA  NA          0
123 NA  NA          60
123 NA  inactive    0
123 NA  inactive    0
222 NA  inactive    0
222 NA  inactive    37
123 NA  inactive    0
123 NA  inactive    60
123 NA  inactive    0
123 NA  inactive    0
dialled     Ringing