Dear Mailing List
I have a data set (data4) consisting of a number of factors and a response
variable. I wish to randomly sample from a combination of two of those factors
(GIS_station and Distance_code2) and return a new dataframe containing the
original data structure (i.e. all the columns) but only containing the randomly
selected rows. The number of rows in each combination of GIS_station and
Distance_code2 vary (widely) and some combinations are absent.
This is getting there::
with (data4,{
sub_sample10=by(data4,list(GIS_station,Distance_code2), function(x)
{sample(1:nrow(x),10,replace=T)})
})
....but just generates two random numbers from the range 1:nrow(x). It doesn't
return the selected rows, which is what I want.
I'm sure I could this could be done in an elegant manner, using a subscript e.g.
sub_sample10 = data4 [sample (1:nrow (data4), size=10), ]
only somehow combining it with the 'by' statement (e.g. by (data4, list
(GIS_station, Distance_code2).......)) but I cannot get this to work.
Any guidance on this much appreciated.
Thankyou.
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