R help - May 2010 - how to select rows per subset in a data frame that are max. w.r.t. a column

Hi,


I'd like to select one row in a data frame per subset which is maximal for a
particular value. I'm pretty close to the solution in the sense that I can
easily select the maximal values per subset using "aggregate", but I
can't
really figure out how to select the rows in the original data frame that are
associated with these maximal values.


library(stats)
# this returns the list with maximal values for breaks per wool/tension
subset
maxValues = aggregate(warpbreaks$breaks, list(wool = wool, tension tension),
max)

# now i'd like the subset of the rows in warpbreaks that are associated with
these maximal values



Thank you in advance!

Tim.

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Hi,

Maybe it's just me but I don't understand what you're trying to do.
Isn't maxValues what you need?
Providing a reproducible example with your data (using the function 
dput), the desired output, and the code you've tried would really help!

Ivan

Le 5/18/2010 10:58, Tim Van den Bulcke a ?crit :
> Hi,
>
>
> I'd like to select one row in a data frame per subset which is maximal
for a
> particular value. I'm pretty close to the solution in the sense that I
can
> easily select the maximal values per subset using "aggregate",
but I can't
> really figure out how to select the rows in the original data frame that
are
> associated with these maximal values.
>
>
> library(stats)
> # this returns the list with maximal values for breaks per wool/tension
> subset
> maxValues = aggregate(warpbreaks$breaks, list(wool = wool, tension >
tension), max)
>
> # now i'd like the subset of the rows in warpbreaks that are associated
with
> these maximal values
>
>
>
> Thank you in advance!
>
> Tim.
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> 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.
>
>    
-- 
Ivan CALANDRA
PhD Student
University of Hamburg
Biozentrum Grindel und Zoologisches Museum
Abt. S?ugetiere
Martin-Luther-King-Platz 3
D-20146 Hamburg, GERMANY
+49(0)40 42838 6231
ivan.calandra at uni-hamburg.de

**********
http://www.for771.uni-bonn.de
http://webapp5.rrz.uni-hamburg.de/mammals/eng/mitarbeiter.php

Hi:

Here are a couple of ways using the doBy and plyr packages:

library(doBy)
library(plyr)

# doBy:
subsetBy(~ wool + tension, subset = breaks == max(breaks), data warpbreaks)

    breaks wool tension
A|H     43    A       H
A|L     70    A       L
A|M     36    A       M
B|H     28    B       H
B|L     44    B       L
B|M     42    B       M

# plyr
ddply(warpbreaks, .(wool, tension), subset, breaks == max(breaks))

  breaks wool tension
1     70    A       L
2     36    A       M
3     43    A       H
4     44    B       L
5     42    B       M
6     28    B       H

HTH,
Dennis

On Tue, May 18, 2010 at 1:58 AM, Tim Van den Bulcke <
vandenbulcketim@gmail.com> wrote:
> Hi,
>
>
> I'd like to select one row in a data frame per subset which is maximal
for
> a
> particular value. I'm pretty close to the solution in the sense that I
can
> easily select the maximal values per subset using "aggregate",
but I can't
> really figure out how to select the rows in the original data frame that
> are
> associated with these maximal values.
>
>
> library(stats)
> # this returns the list with maximal values for breaks per wool/tension
> subset
> maxValues = aggregate(warpbreaks$breaks, list(wool = wool, tension >
tension), max)
>
> # now i'd like the subset of the rows in warpbreaks that are associated
> with
> these maximal values
>
>
>
> Thank you in advance!
>
> Tim.
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> 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.
>
	[[alternative HTML version deleted]]