R help - Sep 2012 - How to convert the output of tapply() so that it has the same order as the input?

Hi,

I try to apply a function to subsets of a data.frame. tapply() does the job, but
the as output, I am looking for a vector (not an array/matrix) ordered in the
same way as the original data, so I can simply cbind the result to the original
data.frame. Below is a minimal example.

I know that there are packages that can do these things easier, but I'm
looking
for a fast solution not requiring additional packages. 

Cheers,

Marius


## data.frame
set.seed(1)
(x <- data.frame(x1=LETTERS[1:4], x2=1:2, value=runif(8)))

## apply a function to each subset combination of x1 and x2
y <- tapply(x$value, x[,-3], function(x) x)

## (trials of) transforming the output to be of the same type and order as
x$value
(y. <- do.call(rbind, y)) # => wrong order
(y. <- do.call(cbind, y)) # => wrong order

## appending (that's the goal)
z <- x
z$value <- y.

Does ave() do what you want?
  y. <- ave(x$value, x$x1, x$x2, FUN=function(x)x)

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at
r-project.org] On Behalf
> Of Marius Hofert
> Sent: Saturday, September 15, 2012 11:07 AM
> To: R-help
> Subject: [R] How to convert the output of tapply() so that it has the same
order as the
> input?
> 
> Hi,
> 
> I try to apply a function to subsets of a data.frame. tapply() does the
job, but
> the as output, I am looking for a vector (not an array/matrix) ordered in
the
> same way as the original data, so I can simply cbind the result to the
original
> data.frame. Below is a minimal example.
> 
> I know that there are packages that can do these things easier, but I'm
looking
> for a fast solution not requiring additional packages.
> 
> Cheers,
> 
> Marius
> 
> 
> ## data.frame
> set.seed(1)
> (x <- data.frame(x1=LETTERS[1:4], x2=1:2, value=runif(8)))
> 
> ## apply a function to each subset combination of x1 and x2
> y <- tapply(x$value, x[,-3], function(x) x)
> 
> ## (trials of) transforming the output to be of the same type and order as
x$value
> (y. <- do.call(rbind, y)) # => wrong order
> (y. <- do.call(cbind, y)) # => wrong order
> 
> ## appending (that's the goal)
> z <- x
> z$value <- y.
> 
> ______________________________________________
> 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,

If you do not want the change the row order or column order, ddply() may be
helpful:
library(plyr)
new1<-ddply(x,.(x1,x2),function(x) x$value)
unlist(list(new1$V1,new1$V2))
#[1] 0.2655087 0.3721239 0.5728534 0.9082078 0.2016819 0.8983897 0.9446753
#[8] 0.6607978
A.K.



----- Original Message -----
From: Marius Hofert <marius.hofert at math.ethz.ch>
To: R-help <r-help at stat.math.ethz.ch>
Cc: 
Sent: Saturday, September 15, 2012 2:07 PM
Subject: [R] How to convert the output of tapply() so that it has the same order
as the input?

Hi,

I try to apply a function to subsets of a data.frame. tapply() does the job, but
the as output, I am looking for a vector (not an array/matrix) ordered in the
same way as the original data, so I can simply cbind the result to the original
data.frame. Below is a minimal example.

I know that there are packages that can do these things easier, but I'm
looking
for a fast solution not requiring additional packages. 

Cheers,

Marius


## data.frame
set.seed(1)
(x <- data.frame(x1=LETTERS[1:4], x2=1:2, value=runif(8)))

## apply a function to each subset combination of x1 and x2
y <- tapply(x$value, x[,-3], function(x) x)

## (trials of) transforming the output to be of the same type and order as
x$value
(y. <- do.call(rbind, y)) # => wrong order
(y. <- do.call(cbind, y)) # => wrong order

## appending (that's the goal)
z <- x
z$value <- y.

______________________________________________
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.