On Aug 7, 2012, at 9:28 PM, arun wrote:
HI,
Try this:
fun1<-function(x,.expr){
.expr<-expression(list(mean.z=mean(z),sd.z=sd(z)))
z1<-eval(.expr)
}
#or
fun1<-function(x,.expr){
.expr<-expression(list(mean.z=mean(z),sd.z=sd(z)))
z1<-.expr
}
dat[,eval(z1),list(x)]
dat[,eval(z1),list(y)]
dat[,eval(z1),list(x,y)]
I'm not seeing the connection between those functions and the
data.table call. (Running that code produces an error on my machine.)
If the goal is to have an expression result then just create it with
expression(). In the example:
> flist <- expression( list(mean.z = mean(z), sd.z = sd(z)) )
> dat[ , eval(flist), list(x)]
x mean.z sd.z
1: 2 0.04436034 1.039615
2: 3 -0.06354504 1.077686
3: 1 -0.08879671 1.066916
--
David.
A.K.
----- Original Message -----
From: Elliot Joel Bernstein <elliot.bernst...@fdopartners.com>
To: r-help@r-project.org
Cc:
Sent: Tuesday, August 7, 2012 5:36 PM
Subject: [R] Repeated Aggregation with data.table
I have been using ddply to do aggregation, and I frequently define a
single aggregation function that I use to aggregate over different
groups. For example,
require(plyr)
dat <- data.frame(x = sample(3, 100, replace=TRUE), y = sample(3, 100,
replace = TRUE), z = rnorm(100))
f <- function(x) { data.frame(mean.z = mean(x$z), sd.z = sd(x$z)) }
ddply(dat, "x", f)
ddply(dat, "y", f)
ddply(dat, c("x", "y"), f)
I recently discovered the data.table package, which dramatically
speeds up the aggregation:
require(data.table)
dat <- data.table(dat)
dat[, list(mean.z = mean(z), sd.z = sd(z)), list(x)]
dat[, list(mean.z = mean(z), sd.z = sd(z)), list(y)]
dat[, list(mean.z = mean(z), sd.z = sd(z)), list(x,y)]
But I can't figure out how to save the aggregation function
"list(mean.z = mean(z), sd.z = sd(z))" as a variable that I can reuse,
similar to the function "f" above. Can someone please explain how to
do that?
Thanks.
- Elliot
--
Elliot Joel Bernstein, Ph.D. | Research Associate | FDO Partners, LLC
134 Mount Auburn Street | Cambridge, MA | 02138
Phone: (617) 503-4619 | Email: elliot.bernst...@fdopartners.com
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______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
Alameda, CA, USA
______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
