Hi Sean,
Here is one option that I believe does what you want. The logic is simple,
1) instatiate a test value that does not meet your criteria
2) use a while loop that will keep looping until your criteria is met
(be sure you set a meetable criteria or this will continue ad
nauseum!!!),
3) randomly select a starting point from all rows except the last 40
(because if it started there, you could not have a consecutive block
of 40, unless you allow wrapping to the beginning in which case you
need to say that).
n <- nrow(yourdata)
test <- 0
while (test < 5) {
i <- sample(1:(n - 40), 1)
x <- yourdata[seq(from = i, to = i + 40), ]
test <- sum(x[, "dp2"])
}
Hope this helps,
Josh
On Thu, Jul 21, 2011 at 1:16 PM, Sean Bignami <bignam...@gmail.com> wrote:
> 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!
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
--
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
https://joshuawiley.com/
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