[R] Why is my data always imported as a list?

[R. Michael Weylandt]

They aren't quite lists --- they are actually data.frame()s which are
a special sort of list with rownames and other nice things.

To your immediate question, I think you're looking for the formula interface:

boxplot(Value ~ State.Fips, data = CB_un)

The data= argument is important so boxplot knows where to look for
"Value" and "State.Fips"

Best,
Michael

On Mon, Jun 11, 2012 at 11:29 AM, Samantha Sifleet
<Sifleet.Samantha at epamail.epa.gov> wrote:
> Hi,
>
> I am a relatively new to R. So, this is probably a really basic issue that
> I keep hitting.
>
> I read my data into R using the read.csv command:
>
> x = rep("numeric", 3)
> CB_un=read.csv("Corn_Belt_unirr.csv", header=TRUE, colClasses=c("factor",
> x))
>
> # I have clearly told R that I have one factor variable and 3 numeric
> variables in this table.
> #but if I try to do anything with them, I get an error
>
> boxplot(CB_un["Value"]~CB_un["State.Fips"])
>
> Error in model.frame.default(formula = CB_un["Value"] ~
> CB_un["State.Fips"]) :
>  invalid type (list) for variable 'CB_un["Value"]'
>
> # Because  these variables are all stored as lists.
> #So, I have to unpack them.
>
> CB_unirr_rent<-as.numeric(unlist(CB_un["Value"]))
> CB_unirr_State<-as.factor(unlist(CB_un["State.Fips"]))
>
> #before I can do anything with them
>
> boxplot(CB_unirr_rent~CB_unirr_State)
>
> Is there a reason my data is always imported as lists?  Is there a way to
> skip this upacking step?
>
> Thanks,
>
> Sam
>        [[alternative HTML version deleted]]
>
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