[R] Removal/selecting specific rows in a dataframe conditional on 2 columns

[R. Michael Weylandt]

Perhaps use tapply() to split by the survey unit and write a little
identity function that returns only those rows you want, then patch
them all back together with something like simplify2array().

Michael

On Tue, Nov 1, 2011 at 1:16 PM, Aurelie Cosandey Godin <godina at 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: godina at dal.ca
>
>
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>
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