faster version of split()?

Hi all,

I want to calculate the number of unique observations of "y" in each 
level of "x" from my data frame "df".

this does the job but it is very slow for this big data frame (159503 
rows, 11 columns).....

group.list <- split(df$y,df$x)
count <- function(x) length(unique(na.omit(x)))
sapply(group.list, count, USE.NAMES=TRUE)

I couldnt find the answer searching for "slow split" and "split time" on 
help forum.

I am running R version 2.2.1, on a machine with 4gb of memory and I'm 
using windows 2000.

thanks in advance,

Simon.







----- Original Message ----- From: "Wacek Kusnierczyk" 
<Waclaw.Marcin.Kusnierczyk at idi.ntnu.no>
To: "Gundala Viswanath" <gundalav at gmail.com>
Cc: "R help" <R-help at stat.math.ethz.ch>
Sent: Friday, January 16, 2009 9:30 AM
Subject: Re: [R] Value Lookup from File without Slurping

you might try to iteratively read a limited number of line of lines in a
batch using readLines:

# filename, the name of your file
# n, the maximal count of lines to read in a batch
connection = file(filename, open="rt")
while (length(lines <- readLines(con=connection, n=n))) {
  # do your stuff here
}
close(connection)

?file
?readLines

vQ


Gundala Viswanath wrote:

Dear all,

I have a repository file (let's call it repo.txt)
 that contain two columns like this:

# tag  value
AAA    0.2
AAT    0.3
AAC   0.02
AAG   0.02
ATA    0.3
ATT   0.7

Given another query vector

qr <- c("AAC", "ATT")

I would like to find the corresponding value for each query above,
yielding:

0.02
0.7

However, I want to avoid slurping whole repo.txt into an object (e.g. 
hash).
Is there any ways to do that?

The reason I want to do that because repo.txt is very2 large size
(milions of lines,
with tag length > 30 bp),  and my PC memory is too small to keep it.