[R] Pass Conditional & loop argument into a function

[Rui Barradas]

Hello,

The other problem with the boxplot question is that it's ill defined. 
Those data[,1], ..., data[, n] variables, what are they? All of them 
numeric? If so, then where is the factor?

Some time ago there was a question on multiple boxplots with cut() 
defining the factor. I wrote a beneral purpose function as an answer:

https://www.stat.math.ethz.ch/pipermail/r-help/2012-July/317991.html

# Example use.
n <- 200
set.seed(1920)
ID <- rep(LETTERS[1:4], n/4)
x <- matrix(runif(3*n, max=rep(c(2, 1, 1.5), each=n)), ncol=3)
DF <- data.frame(ID=ID, x=x)

cols <- grep("x", names(DF)) # something variable
multi.boxplot(DF[, cols], DF$ID, col = rainbow(3))


Hope this helps,

Rui Barradas

Em 08-08-2012 14:43, S Ellison escreveu:
> First thing; are you trying to fit a model specified as
>
> y ~ X + X^2 + X^3 ?
>
> ... because if you are you're unlikely to get anything useful. That uses formula syntax in which ^ does not have the arithmetic power meaning; see section 11.1 'Defining statistical models; formulae' in 'an introduction to R' in your HTML help system. This formula only specifies one term, X, so all you'll get is the result of
>
> y ~ X
>
> If you wanted to fit a polynomial the hard (and not generally good) way you'd have to do
>
> y ~ I(X )+ I(X^2) + I(X^3)
>
> Next, in your line
>   fit <- lm(Y~conditional.argument)
>
> you have asked lm to fit Y to a character string formed by paste(). That is also unlikely to be useful. You would need to create the complete formula as a string (eg "Y~X+I(X^2)+I(X^3)" ) and then use as.formula to convert that to a formula lm can use.
>
> Then there's the unnecessary loop. You can get your formula string without a loop from an integer 'degree' using
>
> formstring <- paste("Y ~ ", paste("I(X^",1:degree,")" , sep="", collapse=" + "))
>
> And then you can convert formstring to a formula object and use the formula object in lm:
> form <- as.formula(formstring) #be careful with this; it looks for the terms in the current environment...
> lm(form)
>
>
> Or, if 'degree' were a vector (say
> degree<-c(1, 3, 5)
> formstring <- paste("Y ~ ", paste("I(X^",degree,")" , sep="", collapse=" + "))
> and so on.
>
>> I am having this problem as well when I want to do a boxplot
>> with variable number of groups to compare.
> I don't know what you're trying to achieve with boxplot, but if you gave boxplot itself your vectors it would plot them by itself:
>
> x<-rnorm(17)
> y<-runif(23)
> z<-c(x,y)
>
> boxplot(x,y,z)
>
> Incidentally, this:
> conditional.argument <- data[,1], data[,2], ...,data[,nvariables]          #
> is not a valid assignment in R, so it cannot be the code you used. And using something called 'data' (or any other object) in a function that does not have an named argument by the same name is asking for trouble; there is no telling where it will get 'data' from but there is a very good chance it will sometimes be from somewhere you don't expect.
>
>
> S Ellison
>   
>> -----Original Message-----
>> I am sure that my approach is kind of stupid but I cannot
>> think of another way to do it. I apologize...
>>
>> foo <- function(..., degree=..){
>>    degree<-3 # example
>>    
>>    conditional.argument <- rep(NA,degree)
>>    for(i in 1:(degree-1)) conditional.argument[i] <-
>> paste("X^",i,"+",sep="")
>>    conditional.argument[degree] <- paste("X^",degree,sep="")
>>    conditional.argument <- paste(conditional.argument,collapse="")
>>    
>>    conditional.argument
>> #  "X^1+X^2+X^3"
>>
>>    fit <- lm(Y~conditional.argument)
>>    ...
>>    return(fit)
>> }
>>
>> I know that there is the poly() function which I am not looking for.
>> I am having this problem as well when I want to do a boxplot
>> with variable number of groups to compare.
>>
>> multiple.boxplot <- function(...,nvariables){
>> conditional.argument <- data[,1], data[,2],
>> ...,data[,nvariables]          #
>> should look like that in the end
>> boxplot(conditional.argument)
>> }
>>
>> Can anyone give me a hint?
>> Daniel Hoop
>>
>>
>>
>>
>> --
>> View this message in context:
>> http://r.789695.n4.nabble.com/Pass-Conditional-loop-argument-i
>> nto-a-function-tp4639580.html
>> Sent from the R help mailing list archive at Nabble.com.
>>
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