[R] Select Random Rows from a dataframe
Sean Bignami
bignami83 at gmail.com
Thu Jul 21 22:16:49 CEST 2011
Hi all,
I have a dataframe of behavioral observations from 360 fish, each with 241 observation points(rows), which looks like this:
> head(d)
fish treatment tank trial video tid pid ang.chg abs.ac t len vel d2p x y
1 1 3 1 1 1 1 1 NA NA 0.0 0.000 NA NA 5.169 9.617
2 1 3 1 1 1 1 2 NA NA 0.5 0.203 0.405 0.203 5.254 9.433
3 1 3 1 1 1 1 3 -78.69660 78.69660 1.0 0.321 0.238 0.119 5.184 9.337
4 1 3 1 1 1 1 4 -29.58347 29.58347 1.5 0.648 0.653 0.327 5.147 9.013
5 1 3 1 1 1 1 5 140.96235 140.96235 2.0 0.988 0.680 0.340 5.434 8.830
6 1 3 1 1 1 1 6 11.52867 11.52867 2.5 1.463 0.949 0.474 5.877 8.660
I have divided it into subsets of "treatment" and "video" types (i.e. dsub.r1 has all treatment 1 and video 1, dsub.s2 all treatment 2, video 2, etc for treatments 1:3 and video1:2)
First: I want to randomly sample a block of 40 consecutive rows from each fish (1-360),
BUT: I can only use that sample if the sum of the "d2p" column for that set of 40 rows is at least 5, otherwise I need to re-sample for another 40-row block, until I get one with a d2p sum of at least 5, if available.
I know how to sample one row, or multiple random rows, but can't figure out how to sample a block of consecutive rows...let alone how to check if the sum of the d2p column is at least 5 and then re-sample if not.
Sadly this is beyond my current knowledge level in R. Please help!!
Thanks in advance!
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