R help - May 2011 - adding columns to dataframes contained in a list

hi there,

I have a list of 5 identical dataframes:

mydf <- data.frame(x=c(1:5), y=c(21:25))
mylist <- rep(list(mydf),5)

and a factor variable with 5 levels:

foo <- c(letters[1:5])
foo <- as.factor(foo)


Question:
I'd like to add a new variable to each dataframe in the list, each
containing only one level of the factor variable. So mylist[[1]]
should have a new variable z containing only "a", in mylist[[2]]  the
new variable z should contain only "b", etc.

(How) can this be done without looping?

All help is greatly appreciated.

Best,
Esther

On Wed, 04-May-2011 at 10:25AM +0300, E Hofstadler wrote:

|> hi there,
|> 
|> I have a list of 5 identical dataframes:
|> 
|> mydf <- data.frame(x=c(1:5), y=c(21:25))
|> mylist <- rep(list(mydf),5)
|> 
|> and a factor variable with 5 levels:
|> 
|> foo <- c(letters[1:5])
|> foo <- as.factor(foo)
|> 
|> 
|> Question:
|> I'd like to add a new variable to each dataframe in the list, each
|> containing only one level of the factor variable. So mylist[[1]]
|> should have a new variable z containing only "a", in mylist[[2]]
the
|> new variable z should contain only "b", etc.
|> 
|> (How) can this be done without looping?

This will work:

zz <- do.call("rbind", mylist)
zz$z <- rep(foo, each = 5)
split(zz, zz$z)

You might want to rename of the list elements if those are
inconvenient.


HTH

|> 
|> All help is greatly appreciated.
|> 
|> Best,
|> Esther
|> 
|> ______________________________________________
|> R-help at r-project.org mailing list
|> https://stat.ethz.ch/mailman/listinfo/r-help
|> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
|> and provide commented, minimal, self-contained, reproducible code.

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