[R] Selecting subset of factor levels

[B Jessop]

Dear r-help,

 

I would like to select a subset of levels from a factor variable in a data frame and return a data frame.

 

The data set consists of 3 variables, 2 of which are factors (Site, Fish) and one numeric (Datavalue) as follows:

 

Site  Fish   Datavalue

AB     2-1    2.3 

AB     2-1    2.4 

AB     2-1    2.2 

AB     2-2    2.6 

AB     2-2    2.5 

AB     2-2    2.7 

AB     2-3    1.6 

AB     2-3    1.5 

AB     2-3    1.4 

etc

AB     2-20   3.1 

AB     2-20   2.9 

AB     2-20   3.0 

 

I would like to create a subset containing all variable rows but for only, say, Fish 2-1, 2-2, and 2-3.  The following code:

 

Df2 <- subset(Df1, Eel=="2-1" | Eel=="2-3") selects only Eel 2-1 and 2-3.  The use of a ":" rather than "|" gives an error message.  My other approaches did not work.  Any 

 

suggestions for doing this task would be much appreciated.

 

Regards,

BJ