[R] providing a variable as a parameter in a function
Subramanian Karthikeyan
Subramanian_Karthikeyan at hc-sc.gc.ca
Wed Oct 22 19:31:30 CEST 2003
>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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