[R] Transforming a string to a variable's name? help me newbie...

[tsunhin wong]

I did really want to find make the suggestion work... it is going to
save my time...
I worked on trying to put all dataframes into a list() by:
###start of file
rm(list=ls())
setwd("/Users/John/Programs/R")
load("Expt108Master2008.Rdata")

nms <- ls(pattern=".data")
my.data <- list()
for(i in nms) my.data[[i]] <- get(i)

save(list=ls(pattern="my."), file="Expt108One.Rdata")
###end of file

The original Rdata file (with global dataframes) is 427.4Mb, and the
new Rdata file with 1 list() storing all dataframes is 427.2Mb
I can now access the individual dataframes by:
my.data$019v1msa1.data

But...
At the moment, whenever I type
>my.data
then the whole huge list of dataframes just flush out of standard
output... and doing a
>dim(my.data)
will give me only NULL...
what command(s) allows me to look at what variables / dataframes are
stored in a list() structure? And how many of them is there?

Thanks a lot! I'm still seasoning my style of working in R!

Regards,

      John

On Mon, Dec 8, 2008 at 4:10 PM, Greg Snow <Greg.Snow at imail.org> wrote:
> I really don't understand your concern.  Something like:
>
>> nms <- c('file1','file2','file3')
>> my.data <- list()
>> for (i in nms) my.data[[ i ]] <- read.table(i)
>
> Will read in the files listed in the nms vector and put them into the list my.data (each data frame is a single element of the list).  This list will not take up about the same amount of memory as if you read each file into a dataframe in the global environment.  And there is no transforming of data frames (into 1 row or otherwise).
>
> --
> Gregory (Greg) L. Snow Ph.D.
> Statistical Data Center
> Intermountain Healthcare
> greg.snow at imail.org
> 801.408.8111
>
>
>> -----Original Message-----
>> From: tsunhin wong [mailto:thjwong at gmail.com]
>> Sent: Monday, December 08, 2008 1:34 PM
>> To: Greg Snow
>> Cc: Jim Holtman; r-help at r-project.org; jorgeivanvelez at gmail.com
>> Subject: Re: [R] Transforming a string to a variable's name? help me
>> newbie...
>>
>> I want to combine all dataframes into one large list too...
>> But each dataframe is a 35 columns x varying number of rows structure
>> (from 2000 to >9000 rows)
>> I have ~1500 dataframes of these to process, and that add up to >
>> 1.5Gb of data...
>>
>> Combining dataframes into a single one require me to transform each
>> single dataframe into one line, but I really don't have a good
>> solution for the varying number of rows scenario... And also, I don't
>> want to stall my laptop every time I run the data set: maybe I can do
>> that when my prof give me a ~ 4Gb ram desktop to run the script ;)
>>
>> Thanks! :)
>>
>> - John
>>
>> On Mon, Dec 8, 2008 at 1:36 PM, Greg Snow <Greg.Snow at imail.org> wrote:
>> > In the long run it will probably make your life much easier to read
>> all the dataframes into one large list (and have the names of the
>> elements be what your currently name the dataframes), then you can just
>> use regular list indexing (using [[]] rather than $ in most cases)
>> instead of having to worry about get and assign and the
>> risks/subtleties involved in using those.
>> >
>> > Hope this helps,
>> >
>> > --
>> > Gregory (Greg) L. Snow Ph.D.
>> > Statistical Data Center
>> > Intermountain Healthcare
>> > greg.snow at imail.org
>> > 801.408.8111
>> >
>> >
>> >> -----Original Message-----
>> >> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
>> >> project.org] On Behalf Of tsunhin wong
>> >> Sent: Monday, December 08, 2008 8:45 AM
>> >> To: Jim Holtman
>> >> Cc: r-help at r-project.org
>> >> Subject: Re: [R] Transforming a string to a variable's name? help me
>> >> newbie...
>> >>
>> >> Thanks Jim and All!
>> >>
>> >> It works:
>> >> tmptrial <- trialcompute(trialextract(
>> >> get(paste("t",tmptrialinfo[1,2],tmptrialinfo[1,16],".gz",sep="")) ,
>> >> tmptrialinfo[1,32],secs,sdm),secs,binsize)
>> >>
>> >> Can I use "assign" instead? How should it be coded then?
>> >>
>> >> Thanks!
>> >>
>> >> - John
>> >>
>> >> On Mon, Dec 8, 2008 at 10:40 AM, Jim Holtman <jholtman at gmail.com>
>> >> wrote:
>> >> > ?get
>> >> >
>> >> >
>> >> > Sent from my iPhone
>> >> >
>> >> > On Dec 8, 2008, at 7:11, "tsunhin wong" <thjwong at gmail.com> wrote:
>> >> >
>> >> >> Dear all,
>> >> >>
>> >> >> I'm a newbie in R.
>> >> >> I have a 45x2x2x8 design.
>> >> >> A dataframe stores the metadata of trials. And each trial has its
>> >> own
>> >> >> data file: I used "read.table" to import every trial into R as a
>> >> >> dataframe (variable).
>> >> >>
>> >> >> Now I dynamically ask R to retrieve trials that fit certain
>> >> selection
>> >> >> criteria, so I use "subset", e.g.
>> >> >> tmptrialinfo <- subset(trialinfo, (Subject==24 &
>> >> Filename=="v2msa8"))
>> >> >>
>> >> >> The name of the dataframe / variable of an individual trial can
>> be
>> >> >> obtained using:
>> >> >> paste("t",tmptrialinfo[1,2],tmptrialinfo[1,16],".gz",sep="")
>> >> >> Then I get a string:
>> >> >> "t24v2msa8.gz"
>> >> >> which is of the exact same name of the dataframe / variable of
>> that
>> >> >> trial, which is:
>> >> >> t24v2msa8.gz
>> >> >>
>> >> >> Can somebody tell me how can I change that string (obtained from
>> >> >> "paste()" above) to be a usable / manipulable variable name, so
>> that
>> >> I
>> >> >> can do something, such as:
>> >> >> (1)
>> >> >> tmptrial <- trialcompute(trialextract(
>> >> >> paste("t",tmptrialinfo[1,2],tmptrialinfo[1,16],".gz",sep="")
>> >> >> ,tmptrialinfo[1,32],secs,sdm),secs,binsize)
>> >> >> instead of hardcoding:
>> >> >> (2)
>> >> >> tmptrial <-
>> >> >>
>> >>
>> trialcompute(trialextract(t24v2msa8.gz,tmptrialinfo[1,32],secs,sdm),sec
>> >> s,binsize)
>> >> >>
>> >> >> Currently, 1) doesn't work...
>> >> >>
>> >> >> Thanks in advance for your help!
>> >> >>
>> >> >> Regards,
>> >> >>
>> >> >>     John
>> >> >>
>> >> >> ______________________________________________
>> >> >> 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.
>> >> >
>> >>
>> >> ______________________________________________
>> >> 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.
>> >
>