How to get minimum value by group

I'd like to get a long data set of minimum values from groups in  
another data
set.
The following almost does what I want. (Note, I'm using the word  
factor
differently from it's meaning in R; bad choice of words)

myframe = data.frame(factor1 = rep(1:2,each=8), factor2 =
rep(c("a","b"),each=4, times=2), factor3 = rep(c("x","y"),each=2,  
times=4),
y=1:16)
attach(myframe)

minimums = by(y, list(factor1, factor2,factor3), min)
detach(myframe)

The problem is that "minimums" is object of class "by", which looks  
like
some kind of array with the number of dimension equal to the number of
factors. I just want two dimensions though, with factors in columns.  
I can't
figure out how to reformat it to something like this:

factor1 factor2 factor2 y
1         a         x         1
2         a         x         9
1         b         x         5
...

I could make nested for loops, but I'd like something that will work  
for an
arbitrary number of factors. I've seen some functions that will  
rearrange
data (e.g. reshape), but they all seem to require a data.frame to  
start
with.
-- 

-----Original Message-----
From: r-help-bounces at r-project.org 
[mailto:r-help-bounces at r-project.org] On Behalf Of JustinNabble
Sent: Tuesday, 12 January 2010 1:58 p.m.
To: r-help at r-project.org
Subject: [R] How to get minimum value by group


I'd like to get a long data set of minimum values from groups 
in another data set.
The following almost does what I want. (Note, I'm using the 
word factor differently from it's meaning in R; bad choice of words)

myframe = data.frame(factor1 = rep(1:2,each=8), factor2 = 
rep(c("a","b"),each=4, times=2), factor3 = 
rep(c("x","y"),each=2, times=4),
y=1:16)
attach(myframe)
minimums = by(y, list(factor1, factor2,factor3), min)
detach(myframe)

The problem is that "minimums" is object of class "by", which 
looks like some kind of array with the number of dimension 
equal to the number of factors. I just want two dimensions 
though, with factors in columns. I can't figure out how to 
reformat it to something like this:

factor1 factor2 factor2 y
1         a         x         1
2         a         x         9
1         b         x         5
...

I could make nested for loops, but I'd like something that 
will work for an arbitrary number of factors. I've seen some 
functions that will rearrange data (e.g. reshape), but they 
all seem to require a data.frame to start with.
--
View this message in context: 
http://n4.nabble.com/How-to-get-minimum-value-by-group-tp10117
45p1011745.html
Sent from the R help mailing list archive at Nabble.com.

aggregate(myframe[4], myframe[1:3], min)

I'd like to get a long data set of minimum values from groups in another data
set.
The following almost does what I want. (Note, I'm using the word factor
differently from it's meaning in R; bad choice of words)

myframe = data.frame(factor1 = rep(1:2,each=8), factor2 =
rep(c("a","b"),each=4, times=2), factor3 = rep(c("x","y"),each=2, times=4),
y=1:16)
attach(myframe)
minimums = by(y, list(factor1, factor2,factor3), min)
detach(myframe)

The problem is that "minimums" is object of class "by", which looks like
some kind of array with the number of dimension equal to the number of
factors. I just want two dimensions though, with factors in columns. I can't
figure out how to reformat it to something like this:

factor1 factor2 factor2 y
1 ? ? ? ? a ? ? ? ? x ? ? ? ? 1
2 ? ? ? ? a ? ? ? ? x ? ? ? ? 9
1 ? ? ? ? b ? ? ? ? x ? ? ? ? 5
...

I could make nested for loops, but I'd like something that will work for an
arbitrary number of factors. I've seen some functions that will rearrange
data (e.g. reshape), but they all seem to require a data.frame to start
with.
--
View this message in context: http://n4.nabble.com/How-to-get-minimum-value-by-group-tp1011745p1011745.html
Sent from the R help mailing list archive at Nabble.com.