[R] Help pasting string as object name

[Rob Denniker]

What a very useful package! Thanks for pointing out its existence.

Sadly ?melt is basically useless, but I did find the following quasi-vignette by the author of the reshape package to be quite useful. http://www.jstatsoft.org/v21/i12/paper

Cheers.

> -----Original Message-----
> From: ba208 at exeter.ac.uk
> Sent: Fri, 3 Apr 2009 11:02:31 +0100
> To: bearmarketsrule at inbox.com
> Subject: Re: [R] Help pasting string as object name
> 
> Hi,
> 
> Is this what you want?
> 
> d <- data.frame(density.AL = seq(1, 10),
> 	density.AK = seq(1, 10),  # many others...
> 	Date=letters[1:10]) # dummy example
> 
> library(reshape)
> melt(subset(d, Date == "b"), id="Date")
> 
> 
> BTW, I spotted a few awkward things in your code,
> 
> 
> st <- c("AL", "AK")
> vars <- paste("d$density", st, sep=".") # easier than mapply etc.
> 
> more importantly, in the for loop you should not be incrementing i
> manually (as in a while loop), it's already taken care of by the for{}
> construct.
> 
> 
> 
> HTH,
> 
> baptiste
> 
> On 3 Apr 2009, at 10:40, Rob Denniker wrote:
> 
>> I have a data frame containing monthly observations of the 'density'
>> of each US state, recorded in variables named "density.AL",
>> "density.AK", "density.AZ", and so on for all 50 states. The data
>> frame (called d) also contains a variable called "Date" which is
>> encoded as a string in the format "Jan-09", "Feb-09", etc.
>> 
>> I also have a vector st.list<-c("AL", "AK", "AZ",...) of length 50.
>> 
>> I would like a new dataframe with st.list in one column and the
>> value of "d$density" for that state when d$Date==Feb-09 in another
>> column.
>> 
>> How can I do this?
>> 
>> Here is what I have tried:
>> 
>> names <- rep("d$density",length(st.list))
>> templist <- as.vector(mapply(paste, names, st.list ,sep="."))
>> 
>> d.2<-data.frame()
>> for (i in 1:length(templist)) {
>> d.2$density[i] <- subset(parse(file="",templist[i]),d$Date=="Feb-09")
>> i<-i+1 }   ### hangs!
>> 
>> 
>> Thanks for any help!
>> 
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> 
> _____________________________
> 
> Baptiste Auguié
> 
> School of Physics
> University of Exeter
> Stocker Road,
> Exeter, Devon,
> EX4 4QL, UK
> 
> Phone: +44 1392 264187
> 
> http://newton.ex.ac.uk/research/emag
> ______________________________

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