[R] using names() as a variable in a formula

femke
2004-02-18T20:44:59Z

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
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