HI David,
Thanks for testing.
It's a bit strange. Yesterday, the function was working perfectly. Today, it
is not working in my system. Not sure what happened.
A.K.
----- Original Message -----
From: David Winsemius <dwinsem...@comcast.net>
To: arun <smartpink...@yahoo.com>
Cc: Elliot Joel Bernstein <elliot.bernst...@fdopartners.com>; R help
<r-help@r-project.org>
Sent: Wednesday, August 8, 2012 9:17 AM
Subject: Re: [R] Repeated Aggregation with data.table
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
>
> ______________________________________________
> R-help@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@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.
David Winsemius, MD
Alameda, CA, USA
______________________________________________
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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.
