Does this work?
library('plyr')
# Function to return a data frame if it has one row, else return NULL:
f <- function(d) if(nrow(d) == 1L) d else NULL
> ddply(RV09, .(set, month), f)
record.t trip set month stratum NAFO unit.area time dur.set distance
1 5 913 1 10 351 3O R31 1044 17 9
2 5 913 3 10 340 3O Q31 1800 18 9
3 5 913 4 10 340 3O Q32 2142 17 9
ddply() is an apply-like function that takes a data frame as input and
a data frame as output (hence the dd). The first argument is the data
frame name, the second argument the set of grouping variables and the
third is the function to be called (in this application).
HTH,
Dennis
On Tue, Nov 1, 2011 at 10:16 AM, Aurelie Cosandey Godin <god...@dal.ca> wrote:
> 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: god...@dal.ca
>
>
> [[alternative HTML version deleted]]
>
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