R help - Nov 2011 - For loop to cycle through datasets of differing lengths

I have encountered this problem on several occasions and am not sure how to
handle it. I use for-loops to cycle through datasets. When each dataset is
of equal length, it works fine as I can combine the datasets and have each
loop pick up a different column, but when the datasets are differing
lengths, I am struggling. Here is an example:
A<-1:10
B<-1:15
C<-1:18

Set1<-data.frame(A,runif(10))
Set2<-data.frame(B,runif(15))
Set3<-data.frame(C,runif(18))

for (i in 1:3){
if (i==1) Data<-Set1 else if (i==2) Data<-Set2 else Data<-Set3
dev.new()
plot(Data[,1],Data[,2])
}


I don't always want to plot them and instead do other things, such as fit a
non-linear equation to the dataset, etc. I end up using that "if"
statement
to cycle through the datasets and was hoping there is an easier method.
Maybe one would be to add extra zeros until they are the same length and
then take out the extra zeros in the first step. Any help would be
appreciated.

-----
In theory, practice and theory are the same. In practice, they are not - Albert
Einstein
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On Thu, Nov 3, 2011 at 11:41 AM, Schatzi <adele_thompson at cargill.com>
wrote:
> I have encountered this problem on several occasions and am not sure how to
> handle it. I use for-loops to cycle through datasets. When each dataset is
> of equal length, it works fine as I can combine the datasets and have each
> loop pick up a different column, but when the datasets are differing
> lengths, I am struggling. Here is an example:
> A<-1:10
> B<-1:15
> C<-1:18
>
> Set1<-data.frame(A,runif(10))
> Set2<-data.frame(B,runif(15))
> Set3<-data.frame(C,runif(18))
>
> for (i in 1:3){
> if (i==1) Data<-Set1 else if (i==2) Data<-Set2 else Data<-Set3
> dev.new()
> plot(Data[,1],Data[,2])
> }
>
>
> I don't always want to plot them and instead do other things, such as
fit a
> non-linear equation to the dataset, etc. I end up using that "if"
statement
> to cycle through the datasets and was hoping there is an easier method.
> Maybe one would be to add extra zeros until they are the same length and
> then take out the extra zeros in the first step. Any help would be
> appreciated.
Well, you can start by putting your data sets in a list:

allSets = list(Set1, Set2, Set3)

then in your loop say

Data = allSets[[i]]

and you're done.

If you have an apriori unknown number of data sets, you can use get.
Before the loop you define the names,

setNames = c("Set1", "Set2", "Set3")

Then in the loop, you can use

Data = get(setNames[i])

But I'm not sure why this would be more useful than the list example
unless perhaps if you `load()' previously `save()'d data sets (the
load() function can give you the names of loaded variables). In any
case, if you repeat the same analysis on a number of data sets with
different dimensions, list() is IMHO the way to go.

HTH,

Peter