[R] using names() as a variable in a formula
Sundar Dorai-Raj
sundar.dorai-raj at pdf.com
Wed Feb 18 22:00:48 CET 2004
femke wrote:
> Greetings List,
>
> I'm having some trouble with the use of the names function in a formula. Below is an example of something that works (i.e first line), and the second line is the same formula which doesn't. I want to be able to reference the column of the dataC table so I can run the variogram iteratively with a loop.
>
>
>>v<-variogram(A1~1,loc=~x+y, dataC)
>>v<-variogram(names(dataC[3])~1,loc=~x+y, dataC)
>
> Error in model.frame(formula, rownames, variables, varnames, extras, extranames, :
> invalid variable type
>
> Where dataC looks like:
>
> x y A1 A2 A3
> 1 514030 4793587 0.0 7.9 0.1
> 2 517995 4792516 5.8 5.1 0.0
> 3 514232 4792210 0.0 6.5 0.0
>
> I though initially that it might need some escape character if quotes are added, and tried the following, but it looks ok.
>
>
>>names(dataC[3])
>
> [1] "A1"
>
>>mode(names(dataC[3]))
>
> [1] "character"
>
>>v<-variogram(as.character(names(dataC[3]))~1,loc=~x+y, dataC)
>
> Error in model.frame(formula, rownames, variables, varnames, extras, extranames, :
> invalid variable type
>
>>v<-variogram(as.formula((names(dataC[3]))~1),loc=~x+y, dataC)
>
> Error in model.frame(formula, rownames, variables, varnames, extras, extranames, :
> invalid variable type
>
> I'd greatly appreciate any suggestions for fixing this.
>
> Thanks again,
>
> femke
> [[alternative HTML version deleted]]
>
You're not building a valid formula. Try this:
v <- list()
for(i in 3:5) {
gr <- names(dataC[i])
f <- formula(paste(gr, "1", sep = " ~ "))
v[[gr]] <- variogram(f, loc = ~ x + y, dataC)
}
BTW, since variogram is not in the base package it would also be helpful
in the future if you add that you are using the spatial package.
HTH,
Sundar
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