Function some()
-----Original Message----- From: r-devel-bounces@stat.math.ethz.ch [mailto:r-devel-bounces@stat.math.ethz.ch] On Behalf Of Gabor Grothendieck Sent: Friday, September 17, 2004 12:52 PM To: r-devel@stat.math.ethz.ch Subject: Re: [Rd] Function some() John Fox <jfox <at> mcmaster.ca> writes:
. . .
Its cute but you could do it on vectors and data frames with 2 function calls. First get some test data: data(iris) data(state) # Now we have: head(sample(iris)) # data frame head(sample(data.frame(state.x77))) # matrix head(sample(letters)) # vector
A possible disadvantage of this approach is that it permutes the entire, potentially large, object before picking the presumably small sample.
The only nuisance is that sample samples from the elements of matrices rather than from their rows thereby necessitating the conversion in the middle call to head(sample(...)). Perhaps an alternate suggestion would be to modify sample so it becomes an S3 generic with methods for matrices and data frames such that sample.matrix samples from the rows of a matrix and sample.data.frame samples from the rows of a data.frame. Then (1) the above idiom becomes consistent across the above mentioned classes. (2) This would also avoid burdening the base with an extra function and would (3) provide for the possibility of extending sample to other classes.
This occurred to me, too [as did providing a random argument to head()], but seemed a more radical proposal than introducing a simple new generic. Regards, John
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