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.bernstein at fdopartners.com
On Tue, Aug 7, 2012 at 4:36 PM, Elliot Joel Bernstein <elliot.bernstein at fdopartners.com> wrote:> 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?One exceptionally kludgy way: zzz <- expression(list(mean.z = mean(z), sd.z = sd(z))) dat[, eval(zzz), list(x,y)] Michael> > 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.bernstein at fdopartners.com > > ______________________________________________ > 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.
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)]
A.K.
----- Original Message -----
From: Elliot Joel Bernstein <elliot.bernstein at fdopartners.com>
To: r-help at 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.bernstein at fdopartners.com
______________________________________________
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.