Dear list, 

After reading different mails, blogs, and tried a few different codes without any success, I am asking your help!
I have the following data frame where each row represent a survey unit with the following variables:

> names(RV09)
 [1] "record.t"  "trip"      "set"       "month"     "stratum"   "NAFO"     
 [7] "unit.area" "time"      "dur.set"   "distance"  "operation" "mean.d"   
[13] "min.d"     "max.d"     "temp.d"    "slat"      "slong"     "spp"      
[19] "number"    "weight"    "elat"      "elong"

Each survey unit generates one set record, denoted by a 5 in column "record.t". Each species identified in this particular survey unit generates an additional set record, denoted by a 6. 

> unique(RV09$record.t)
[1] 5 6

Each survey unit are identified by a specific "trip" and "set" number, so if there is a 5 record type with no associated 6 records, it means that no species were observed in that survey unit. I would like to be able to select all and only these survey units, which represent my zeros.

So as an exemple, in this trip number 913, set 1, 3, and 4 would be part of my "zeros" data.frame as they appear with no record.t 6, such that no species were observed in this survey unit.

> head(RV09)
   record.t trip set month stratum NAFO unit.area time dur.set distance
585        5  913   1    10     351   3O       R31 1044      17        9
586        5  913   2    10     351   3O       R31 1440      17        9
587        6  913   2    10     351   3O       R31 1440      17        9
588        5  913   3    10     340   3O       Q31 1800      18        9
589        5  913   4    10     340   3O       Q32 2142      17        9

Any tips on how extract this "zero" data.frame in R? 
Thank you very much in advance!

Best,
~Aurelie


Aurelie Cosandey-Godin
Ph.D. student, Department of Biology
Industrial Graduate Fellow, WWF-Canada
Dalhousie University | Email: godina@dal.ca


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