Any way to add to data frame saved as .rData file?

thx everyone for your help...for simplicity, i elected to stay with a text 
file and transpose it so that each new row of data is really a column...in 
this transposed file, the header is really the row labels. the first cell 
has the name of the row labels ("RowID" in this case)...

here's code for what i ended up doing, in case anyone wants it (or wants to 
improve it) :


outfile <- mydata.txt

zz <- file(outfile, "w")

rowlabels <- c(1:10000)

cat(c("RowID", rowlabels, "\n"), file = zz, sep = "\t")   # make the first 
row of the file have the row labels

grep_text <- function(s)   # 's' is a unique string that is contained in the 
col or cols that you want
{
	temp_header <- scan(file = outfile, what = list("RowID"), flush = TRUE)
	temp_header <- unlist(temp_header)
	g <- grep(toString(s), temp_header)  # gives the row number in outfile with 
the data you want

	if(length(g)==1)
	{
		temp_file <- scan(file = outfile, what = character(), skip = g-1, nlines = 
1)  # temp_file = a vector
		temp_file <- temp_file[2:length(temp_file)]  # drop title
		temp_file <- as.numeric(temp_file)  # now this is num vector
		tf_df <- as.data.frame(temp_file)
	}

	if(length(g)>1)
	{
		for(i in 1:length(g))
		{
			temp_file <- scan(file = outfile, what = character(), skip = g[i]-1, 
nlines = 1)
			temp_file <- temp_file[2:length(temp_file)]  # drop title
			temp_file <- as.numeric(temp_file)  # now this is num vector

			if(i==1)
			{
				tf_df <- as.data.frame(temp_file)
			}

			if(i!=1)
			{
				tf_df[i] <- temp_file
			}
		}
	}

	return(tf_df)
}


you would use grep_text(s) to return a data frame with column titles 
contained in the string s...if i had a column named "Year05_population" in 
the "mydata.txt" file, to return a data frame named 'df' with only that one 
column titles "Year05_population" i would simply type :

outfile <- mydata.txt
df <- grep_text("Year05_population")

From: "Greg Snow" <greg.snow at ihc.com>
To: jerk_alert at hotmail.com,murdoch at stats.uwo.ca
CC: gunter.berton at gene.com,r-help at stat.math.ethz.ch
Subject: Re: [R] Any way to add to data frame saved as .rData file?
Date: Thu, 13 Oct 2005 12:53:10 -0600

Have you looked at the g.data package?  It might be useful
(but may still require some redesign of your dataset).

Greg Snow, Ph.D.
Statistical Data Center, LDS Hospital
Intermountain Health Care
greg.snow at ihc.com
(801) 408-8111

"Ken Termiso" <jerk_alert at hotmail.com> 10/13/05 08:14AM >>>

I'd put the extra columns in their own data frame, and save that to

disk

(use dates/times/process ids or some other unique identifier in the
filenames to distinguish them).  When you need access to a mixture of

columns, load (or source, depending how you did the save) the columns

you

need, and cbind them together into one big data frame.

If you are concerned about memory requirements when producing the

pieces,

watch out that you don't write out so much data that you'll never have

enough memory to load all you need at once.

Duncan Murdoch

hmm...maybe i should just be dumping to a text file instead of a data
frame..is there any way (without using a real SQL database) in R to
create a
file that i can selectively load certain columns from?

if not, maybe i should break the data frame up into pieces (as you
suggested) and create a separate file that keeps track of which columns
are
stored in which files (like a hashtable) and just load the small file
of
keys each time i need to load something..

whaddya think??

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