R help - Oct 2003 - providing a variable as a parameter in a function

>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.

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.
>
>______________________________________________
>R-help at stat.math.ethz.ch mailing list
>https://www.stat.math.ethz.ch/mailman/listinfo/r-help
____________________________
John Fox
Department of Sociology
McMaster University
email: jfox at mcmaster.ca
web: http://www.socsci.mcmaster.ca/jfox

Thanks John,

Your solution worked..

After i posted my message I tried sth else which also worked...

I tried this:

for (i in 3:cnum) {
      fla = as.formula(paste((cnom[i],"~","Trt*Dose"))
      mod = lm(fla, data = x, contrasts = list(Trt = contr.sum, Dose contr.sum))
      an = Anova(mod,type = "III")
      print(an)
      }

but yours is a succint and nice solution.

Thanks again,
Karth.




                      John Fox
                      <jfox at mcmaster.ca        To:       "Subramanian
Karthikeyan" <Subramanian_Karthikeyan at hc-sc.gc.ca>
                      >                        cc:       r-help at
stat.math.ethz.ch
                                               Subject:  Re: [R] providing a
variable as a parameter in a function
                      2003-10-22 02:24
                      PM






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.
>
>______________________________________________
>R-help at stat.math.ethz.ch mailing list
>https://www.stat.math.ethz.ch/mailman/listinfo/r-help
____________________________
John Fox
Department of Sociology
McMaster University
email: jfox at mcmaster.ca
web: http://www.socsci.mcmaster.ca/jfox