Thank you David. I probably didn't make my question clear enough. In the end, I
want a "shorter" version of the original data frame, basically with variable
"rep" removed, then just one row per id, time and mode combination. The
original
data frame has 54 rows, I wish to have a data frame with only 27 rows after
average.
Using ave() would produce the following 3 rows for example:
id time mode rep y avg.y
1 1 0 R 1 -1.089540576 -0.21924078
19 1 0 R 2 -0.743374679 -0.21924078
37 1 0 R 3 1.175192908 -0.21924078
But I only need one row:
id time mode avg.y
1 1 0 R -0.21924078
Thanks again,
John
----- Original Message ----
From: David Winsemius <dwinsem...@comcast.net>
To: array chip <arrayprof...@yahoo.com>
Cc: r-help@r-project.org
Sent: Thu, September 9, 2010 3:21:15 PM
Subject: Re: [R] "sequeeze" a data frame
On Sep 9, 2010, at 5:47 PM, array chip wrote:
> Hi, suppose I have a data frame as below:
>
>dat<-cbind(expand.grid(id=c(1,2,3),time=c(0,3,6),mode=c('R','L'),rep=(1:3)),y=rnorm(54))
>)
>
>
> I kind of want to "squeeze" the data frame into a new one with averaged "y"
>over
> "rep" for the same id, time and mode. taking average is easy with tapply:
>
> tapply(dat$y, list(dat$id, dat$time, dat$mode), mean)
Try:
dat$avg.y <- ave(dat$y, dat$id, dat$time, dat$mode, FUN=mean)
?ave
The syntax of ave is different than "tapply" or "by". The grouping factors are
not presented as a list and the FUN argument comes after the ,..., so it needs
to be named if different than the default of "mean".
>
> But I want the result to be in the same format as "dat". Certainly, we always
> can transform the result (array) into the data frame using a lot of codes. But
> is there a simple way to do this?
>
> Thanks
David Winsemius, MD
West Hartford, CT
______________________________________________
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.
