[R] Using sample to create Training and Test sets
Frank E Harrell Jr
f.harrell at vanderbilt.edu
Fri May 15 14:28:51 CEST 2009
Note that the single split sample technique is not competitive with
other approaches unless the sample size exceeds around 20,000.
Chris Arthur wrote:
> Forgive the newbie question, I want to select random rows from my
> data.frame to create a test set (which I can do) but then I want to
> create a training set using whats left over.
> Example code:
> acc <- read.table("accOUT.txt", header=T, sep = ",", row.names=1)
> #select 400 random rows in data
> training <- acc[sample(1:nrow(acc), 400, replace=TRUE),]
> #try to get whats left of acc not in training
> testset <- acc[-training, ]
> Fails with the following error....
> Error: invalid subscript type
> In addition: Warning message:
> - not meaningful for factors in: Ops.factor(left)
> I then try.
> testset <- acc[!training, ]
> Which gives me the warning message
> ! not meaningful for factors in: Ops.factor(left)
> And if i look at testset It is 400 rows of NA's ... which clearly isn't
> Can anyone tell me what I'm doing wrong.
> Thanks in advance
Frank E Harrell Jr Professor and Chair School of Medicine
Department of Biostatistics Vanderbilt University
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