On Sep 20, 2010, at 1:40 PM, Joshua Wiley wrote:
On Mon, Sep 20, 2010 at 10:27 AM, Phil Spector
<spec...@stat.berkeley.edu> wrote:
Harold -
Two ways that come to mind:
1) do.call(rbind,lapply(split(tmp,tmp$index),function(x)x[1:5,]))
2) subset(tmp,unlist(tapply(foo,index,seq))<=5)
3) do.call(rbind, by(tmp, tmp$index, .Primitive("["), 1:5, 1:2))
I found that rather interesting but somewhat puzzling. I generally
thought that using "[" should "work" but by() was complaining:
Error in FUN(X[[1L]], ...) : could not find function "FUN"
So tried using back-quotes and got a sensible result.
> do.call(rbind, by(tmp, tmp$index, FUN=`[`, 1:5, 1:2))
index foo
1.6 1 -3.0267759
1.7 1 -1.3725536
1.19 1 -1.1476048
1.16 1 -1.0963967
1.2 1 -1.0684793
2.29 2 -1.6601486
2.21 2 -1.2633632
2.22 2 -0.9875626
2.38 2 -0.9515301
2.30 2 -0.8638903
Unlike Dalgaard who arrived at a similar result via a different route
and called the row names "silly", I thought they were informative. But
maybe the sobriquet was directed at his second solution. I couldn't
tell.
--
David.
Josh
- Phil Spector
Statistical Computing
Facility
Department of Statistics
UC Berkeley
spec...@stat.berkeley.edu
On Mon, 20 Sep 2010, Doran, Harold wrote:
Suppose I have a data frame, such as the one below:
tmp <- data.frame(index = gl(2,20), foo = rnorm(40))
And further assume it is sorted by index and then by the variable
foo.
tmp <- tmp[order(tmp$index, tmp$foo) , ]
Now, I want to grab the first N rows of tmp for each index. In the
end,
what I want is the data frame 'result'
tmp1 <- subset(tmp, index == 1)
tmp2 <- subset(tmp, index == 2)
tmp1 <- tmp1[1:5,]
tmp2 <- tmp2[1:5,]
result <- rbind(tmp1, tmp2)
Does anyone see a way to subset and subsequently bind without a
loop?
Harold
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--
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/
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David Winsemius, MD
West Hartford, CT
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