R help - Oct 2003 - passing a variable (containing the value of the argument) to a function

My previous question put in a simpler  way:

How would I pass a value of a variable to a function such as

lm(Effect1~Trt*Dose, data = x, contrasts = list(Trt = contr.sum, Dose
contr.sum))?

Here, 'Effect' is a column name in my data matrix, and I want
"Effect1" to
be replaced by "Effect2" and so on (my other column names in the data
frame) for successive anova calculations. So I am storing the column names
as an array, and passing the array as a parameter to the lm() function.

Thanks,


----- Forwarded by Subramanian Karthikeyan/HC-SC/GC/CA on 2003-10-22 01:47
PM -----

                      Subramanian
                      Karthikeyan              To:       r-help at
stat.math.ethz.ch
                                               cc:
                      2003-10-22 01:31         Subject:  providing a variable as
a parameter in a function
                      PM




>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.

"Subramanian Karthikeyan" <Subramanian_Karthikeyan at
hc-sc.gc.ca> writes:
> My previous question put in a simpler  way:
> 
> How would I pass a value of a variable to a function such as
> 
> lm(Effect1~Trt*Dose, data = x, contrasts = list(Trt = contr.sum, Dose >
contr.sum))?
> 
> Here, 'Effect' is a column name in my data matrix, and I want
"Effect1" to
> be replaced by "Effect2" and so on (my other column names in the
data
> frame) for successive anova calculations. So I am storing the column names
> as an array, and passing the array as a parameter to the lm() function.
A canonical trick is

for (myname in names(myframe)){
  mycall <- substitute(lm(myvar~etc.etc.....),list(myvar=as.name(myname)))
  myfit <- eval(mycall)
  print(summary(myfit))
}

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
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~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907