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

[S Ellison]

Noone has yet mentioned tjhe 'standard' way to reference a data frame item, which uses $

boxplot(CB_un[["Value]]~CB_un[["State.Fips"]])  #Note the double [[ ]]
# is equivalent to
boxplot(CB_un$Value~CB_un$State.Fips)
# and can be achieved by 
boxplot(Value~State.Fips, data=CB_un)

The rather awkward [["name"]] notation is usually only needed if the name does not comply with variable naming requirements (including list and data frame names); for example, names containing spaces or operator symbols (like "+") are not allowed for ordinary variables. It is possible and sometimes useful to create non-standard data frame names for display; for example, anova.lm actually returns a data frame with names "Df", "Sum Sq", "Mean Sq", F value" and "Pr(>F)". But it makes manipulation a tad trickier and you'd be unable to use them in the context of a formula with a data argument. 

S Ellison

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Samantha Sifleet
> Sent: 11 June 2012 17:29
> To: r-help at r-project.org
> Subject: [R] Why is my data always imported as a list?
> 
> 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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