[R] providing a variable as a parameter in a function

[John Fox]

Dear Subramanian,

How about this:

         for (y in df[, 3:5]) {
                 mod = lm(y ~ Trt*Dose, data = x, contrasts = list(Trt = 
contr.sum, Dose = contr.sum))
                 Anova(mod, type = "III")
                 }

Does that give you what you want?

John



At 01:31 PM 10/22/2003 -0400, Subramanian Karthikeyan wrote:
> >From a data frame, how do we extract a specific column name, and plug that
>into a command (eg. for Anova as shown below)
>
> > df = read.delim("mydata.txt")
> > y = colnames(df)
> > r = ncol(x)
>
>Lets say that in the data frame column 1 contains treatments, column 2
>contains doses, and columns 3, 4, 5 etc. are different responses, and I
>want to run separate 2-way anovas for each response, i.e. my first anova
>will be done using col 1: Treatment, col 2: Dose and Col 3: a response,
>second anova will be done using treatment (col1), dose (col2) and another
>response (col 4) and so on.
>
>I could use a loop to automate the task.
>
> > for (i in 3:r) {
>+ mod = lm(y[i]~Trt*Dose, data = x, contrasts = list(Trt = contr.sum, Dose
>= contr.sum))
>+ Anova(mod, type = "III")
>+ }
>
>The problem is when I directly plug in y[3] for my response variables name,
>it gives me an error
>
>Error in model.frame(formula, rownames, variables, varnames, extras,
>extranames,  :
>         invalid variable type
>
>This is likely because the lm() function wants the actual column name,
>rather than a variable containing the column name.
>
>Can someone advice?
>
>Thanks,
>Karth.
>
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____________________________
John Fox
Department of Sociology
McMaster University
email: jfox at mcmaster.ca
web: http://www.socsci.mcmaster.ca/jfox