On Feb 7, 2011, at 11:29 PM, Al Roark wrote:
I'd like to summarize several variables in a data frame, for
multiple groups, and store the results in a data.frame. To do so,
I'm using by(). For example:
df<-
data
.frame
(a
=1:10,b=11:20,c=21:30,grp1=c("x","y"),grp2=c("x","y"),grp3=c("x","y"))
dfsum<-by(df[c("a","b","c")], df[c("grp1","grp2","grp3")], range)
The result has a class of "by" and a mode of "list". I'm new to R
and can't find any documentation on this class, and don't see
methods for it associated with the as.data.frame. How should I go
about coercing this to a data frame? Is there a comprehensive
source that I'm might be missing, which can tell me such things?
I looked it up in Spector's "Data Manipulation":
> do.call(rbind, dfsum)
[,1] [,2]
[1,] 1 29
[2,] 2 30
Your test case is a bit pathological, since there are really only two
"combinations" within your three groups of factors, at least only two
combinations with values. Quite frankly, I have never understood how
by() works and do most of my work with tapply and
Hmisc::formula.describe and aggreagate. Many people have switched over
the plyr package.
Cheers
[[alternative HTML version deleted]]
David Winsemius, MD
West Hartford, CT
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