On Feb 16, 2011, at 11:35 PM, yf wrote:
I want to sample from the ID. For each ID, i want to have 2 set of
data. I
try the sample() function but it didn't work.
You don't say _how_ you used the sample function. You should show what
code you used when stating the _something_ "doesn't work".
Sample returns a vector of items from objects where length()
represents some sensible notion. It does not "sample" a complex object
such as a dataframe. For dataframes, length is the number of columns,
which doesn't agree very well with most people's notion of cases from
which to sample. For selection of rows of a dataframes you need to
first create a vector of numeric indices and then use that with "["
idx <- sample(nrow(x), nrow(x)/2)
# A random split
x[ idx, ]
x[ -idx, ]
x<-data.frame(id=c(1,1,1,2,2,2,2,3,3,3,4,4), v1=c(1:12), V2=c(12:23))
x
id v1 V2
1 1 1 12
2 1 2 13
3 1 3 14
4 2 4 15
5 2 5 16
6 2 6 17
7 2 7 18
8 3 8 19
9 3 9 20
10 3 10 21
11 4 11 22
12 4 12 23
--
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